Battery Life

[Gary_C]

I have been living on my job site in my camper this winter. I have four 6 volt batterys (Trojan T 125's) hooked up in a two bank 12 volt system feeding an inverter. I had replaced all four batterys a year ago January because of a faulty cable connection that caused the batterys to be undercharged and frozen. But back in December when it was really cold, I could not get but 80 amp hours out of the batterys before the controller shut down on low voltage. And when I checked the water levels, there were ice crystals in some of the cells but only at below zero temps.

So at the dealers request I brought the batterys back and he gave them a full charge and I tried them again and still only 80 some amps to discharge levels. So he replaced them and the new ones, don't know the brand but they are white with red tops. and these will put out 180+ amp hours to discharge. But after just about three months of operation, they seem to have dropped to just over 100 amp hours capacity. At the cost of these dang things, this is going to get expensive to replace these things at least every year.

And I do have a Zantrex 2500 watt inverter with a Hart interface/controller that controls the entire charge/discharge cycle. And I also have two 50 watt solar panels and they will charge as much as 7.8 amps in strong sunlight, but that is not in the winter. It was hard to keep them clean of snow and the sun was too low and mostly behind the trees for them to work much in the winter.

Here is a picture of the control setup.





So what kind of life are any of you other off grid people seeing from your battery banks and what kind of batterys are you using?

[doctorb]

I am not off-grid, but I am also disappointed in the battery life I am getting from new 6-volt deep cycle batteries.  We use them in 60 or 72 volt systems for "electric" fishing on our reservoirs, which do not permit gas engines.  We used to get 3-4 years out of a set, and used to have very prolonged run times if you didn't crank it wide open all the time. 

Now, I get 2 seasons max, and my daily run time is decreased.  I have not changed any of the equipement on the boat, and use the same routine for maintenance as I did before.  I can't explain it except to say that they don't seem to build them like they used to.

[John Mc]

How low are you letting the charge get in the batteries? My neighbors have an off grid solar house and are very careful never to let the battery bank drop below 50% state of charge. Generally, they like to not even get it that low. The deeper you cycle lead-acid batteries, the shorter their life.

Also, leaving a battery in a partially discharged state is not good for longevity. If you discharge it, you want to charge it back up as soon as possible.

You may also want to look at a charger that has a "desulferator". Batteries tend to build up "sulfation" over time, which diminishes capacity. You can reverse this, to some extent with the appropriate type of recharger. Doing this as periodic maintenance can help, since if you let it go too far, it can be hard to bring the battery back.

[Gary_C]

That Hart interface completely controls the amount of discharge and will shutdown the inverter at a set voltage level. I can't remember the setting, but I think it is either 10.0 or 10.2 volts which allows use of some percent of capacity. Discharging below that level will shorten the battery life. But I never do that because it automatically dumps the load at the set level.

I was reading on a battery dealers (in Alaska) web site last night and they say that batteries work best at 68 deg F so that is one problem. My battery compartment is in an unheated and ventilated space so this winter those batteries were forced to operat at outside temps of up to 32 below zero at night this winter. On those very cold nights I left the generator run all night but even the generator would be running rough by morning cause the carb iced up in the extreme cold. I may have to find some battery heaters that are supposedly available. I hate to enclose the battery compartment because of the presence of hydrogen gas from the charging.

[wdncno]

We have been using used forklift batteries. Very heavy, but a lot of capacity even when  they will no longer support the 300-500 amp draw of a fork lift.  Also can sometimes be purchased for scrap price.  We got about 5 years of continuous service out of the last set.  That was running a small house and chargering with a generator.

[Dean186]

That Hart interface completely controls the amount of discharge and will shutdown the inverter at a set voltage level. I can't remember the setting, but I think it is either 10.0 or 10.2 volts which allows use of some percent of capacity. Discharging below that level will shorten the battery life. But I never do that because it automatically dumps the load at the set level.

Gary,  

With four Trojan T-125s connected as a 12 volt system, you would have a maximum capacity of 480 amp hours.   Ideally the battery bank should be discharged only to about 60 percent of their capacity, which would be a voltage reading of 12.2 volts.  The voltage reading of 10.0 volts is almost fully discharged and is much to low.  The set point should be no lower than 12.0 volts.  The Trojan T-125s are one of the best deep cycle camper batteries out there IMHO, and they should last about 10 years in a camper.

Since you say you don't remember the exact set point, it most likely is 12.0 or 12.2 volts.  How are you measuring the 80 amp hours of usage?  With a set point of 12.2 volts, one should get a usable 40% of the total 480 amps or 192 amp hours.  This would be a maximum number with new batteries and 100% charge, which can be a challenge.  Real camping numbers would look more like ((90%x480) x 40%) = 172 amp hours of storage capacity.

Hope this makes sense and is of some use.  

Dean

[Dean186]

So what kind of life are any of you other off grid people seeing from your battery banks and what kind of batterys are you using?

Gary,  I thought I would also answer your question more directly, since you mentioned your installation was in a camper.  I have two Trojan T-125 in my camper charged by 160 watts of solar.  I am on my fourth year with this setup and they still perform like new.  I expect them to last several more years.

John Mc makes a good point about battery sulfation.  Sulfation of batteries starts when the voltage drops below 12.2 volts for a 12 volt lead acid battery system. Sulfation hardens on the battery plates reducing and eventually destroys the batteries ability to generate power.   This is why I try to never let my batteries drop below 12.2 volts.

Some chargers have a de-sulfation charge option, which is a controlled overcharge.  The de-sulfation charge can help considerably in some cases.  It is an option that I have on my camper charging system.  Make sure to read the chargers manual before doing the de-sulfation charge.  The important points are the amount of time one should leave the batteries in this state of charge, and to top off water levels before and after charging.

[John Mc]

Some chargers have a de-sulfation charge option, which is a controlled overcharge.

I thought that was known as an "equalization charge". The chargers I've seen that do de-sulfation use a "pulse" technology...

But I have to admit, I have little direct experience with this... just some reading, an dmuch of that was a couple of years ago.

[Gary_C]

Sorry I have not responded sooner, but I was back to work. While I was there, I reviewed the Heart Interface which is the lower black unit in the picture I posted earlier.

According to the instructions. the Heart Interface or Link 1000 controller will shut down the inverter at 10.5 volts. That is supposed to be at 50 % discharge. And it does have an equalize function though I have not used it because I do not have a good way to disconnect all 12 loads to protect them from the high voltages generated during equalizing.

The SEL button allows you to cycle thru four readings. In the picture it is in sleep mode. It shows volts, amps + or -, amp-hours, and time remaining.

With four Trojan T-125s connected as a 12 volt system, you would have a maximum capacity of 480 amp hours.   

Real camping numbers would look more like ((90%x480) x 40%) = 172 amp hours of storage capacity.

I do remember that 480 amp-hours as the maximum capacity and I think you are right that around 180 is a normal capacity. But those Trojan T-125's were only putting out 80 amp-hours to 10.5 volts. And the new US Battery's are normally running over 125 amp-hours to 10.5 volts. And now that has seems to be dropping to closer to 100 amp-hours. And that has been thru the winter when temps were below freezing just about all the time and a few nights down to -30 F. And with the warmer temps and the furnace running less, it seems like it should be better but it's not.

I found a good web page with some battery ratings.     6 Volt Golf Cart Battery: The Top Six


According to that, the Trojan T-105 will give you more cycles but at a slightly lower rating.

It has been a real learning experience this winter living off the grid. I am just thankful that I bought that Honda EU 3000i generator. It has worked flawlessly all winter. Starts instantly and runs great. There was only a couple of nights when it was around -30 F that I had trouble with the carb intake icing up and I had to wrestle the generator inside and unfreeze the carb intake.

I did learn that an electric blanket will work fine on a generator but not at all on an inverter. I don't know why.

[Dean186]

Some chargers have a de-sulfation charge option, which is a controlled overcharge.

I thought that was known as an "equalization charge". The chargers I've seen that do de-sulfation use a "pulse" technology...

But I have to admit, I have little direct experience with this... just some reading, an dmuch of that was a couple of years ago.

John Mc,  You are right; the equalization charge is essentially a controlled over charge and not de-sulfation.   Desulfation uses high frequency electronic pulses.

My MPPT solar controller in my camper provides an equalization charge and not a sulfation option.

Both equalization and desulfation can prove beneficial for flooded/wet cell batteries.   One should not equalize gel or AGM batteries.

[Dean186]

Gary_C,

Charts for battery voltage and how it relates to percent charge can be found on the internet.  Charts on the Trojan website shows 60 percent charge is a voltage reading of 12.24 volts on a 12 volt system.  A battery voltage of 11.51 is 10 percent charge.  

The life of a battery will be significantly reduced when it is discharged to below 50 percent on a regular bases and a 10.2 volt reading is fully discharged.   To me, this explains why the camper batteries aren't lasting very long.

Another thing to consider is; the amp hour rating quoted in the manuals is for warmer temperatures, if I remember correctly it is a 80 degree temperatures rating.  The rating will be less with colder temperatures.  You quoted -30 degrees temperatures - yikes that is cold camping weather.

On the electric blanket, when you say doesn't work, do you mean, there isn't enough amp hours left in the batteries, or it just doesn't function.  If it doesn't function, it could be that it doesn't like anything but a pure sine wave inverter, or at least a good modified sine wave inverter.

Stay warm,  Dean

[Gary_C]

I did just look at that handbook for the Link 1000 controller and thought the 10.5 was right. But now I am not so sure and cant find the manual on line. Perhaps it was 11.5 volts. I will check for sure later this week when I am back there, but of course I have no internet service up there so it may take a while to get back with the right settings.

On the electric blanket, when you try to run it on the inverter it will just buzz and no heat to the blanket. If you leave it on for some time, the control gets warm. It must be the circuits in the controller don't like the wave form of the inverter. And I have an almost new Xantrex 458 inverter that is rated at 3000 watts. It runs the TV, microwave, and other electronic things just fine, but not an electric blanket.

[Ianab]

Re the Electric blanket, sounds like you need an "old school" one with just a simple switch, not an electronic controller?

Ian

[mad murdock]

Gary C, I do not use batteries off grid, but I do know a bit about battery construction, and what factors effect battery service life, etc.  As has been aptly stated, close monitoring of discharge state, and not letting batteries get below a certain level will have a great effect on what usable life one gets out of a battery.  Another thing is battery construction itself.  I am speaking from my experience with 25+ years of aviation maintenance and operation background here.  The best batteries (as far as capacity, discharge/recharge cycle life, and overall performance have plate material that is very pure, and the real expensive batteries will have plates made from solid lead plates, rather than the lead powder pressed plates, with the mesh composite construction.  The solid plates are less susceptible to sulfidation issues, and have a much higher cycle life, the downside is that these type of batteries typically are quite expensive to build, and to buy.  This may or may not be of help to you.  The heavy industrial type batteries make excellent choices for aux. or off grid power systems.  In my area, if a guy can find the telecom batteries that the phone companies discard usually every 2 years, are good to build a system around, as the cells are HUGE, and you can string whatever you want for your system in 1 cell (2 volt) increments.  One of those cells (2 volts) weighs about 40 lbs, they have a ton of capacity, and good cycle life.

[Gary_C]

That's interesting. I may try to find some of those 2 Volt batteries.

[DarkBlack]

Some chargers have a de-sulfation charge option, which is a controlled overcharge.

I thought that was known as an "equalization charge". The chargers I've seen that do de-sulfation use a "pulse" technology...

But I have to admit, I have little direct experience with this... just some reading, an dmuch of that was a couple of years ago.

John Mc,  You are right; the equalization charge is essentially a controlled over charge and not de-sulfation.   Desulfation uses high frequency electronic pulses.

My MPPT solar controller in my camper provides an equalization charge and not a sulfation option.

Both equalization and desulfation can prove beneficial for flooded/wet cell batteries.   One should not equalize gel or AGM batteries.

Hey Dean there you go again :-\ Why do you keep posting as an expert when you obviously are not? Anyone can come back a day later after reading it on the net and then copy and paste it as if they knew it all along. I just don't see why you would want to do it. I mean really why?? If you really don't know something that's OK, you don't have to make it up. You tried to get me into a debate on another post where I already knew you didn't know what you were copying and pasting, That's why I didn't bother to debate with you.

[beenthere]

DB
How about if we just hear your opinion and let it go at that?  : :

[DarkBlack]

DB
How about if we just hear your opinion and let it go at that?  : :

You just got my opinion. :( I think posters should state opinions as opinions, and facts as facts... if they are.
Actually pretty simple.

[doctorb]

DB-

Since your interested in opinons as opinions and facts as facts, I would calmly, respectfully like to say that my opinion is that you seem to miss some of the worth of the Forum, as reflected in your posts.  It's not my Forum, but I can tell you that when bravado and arrogance overwhelm someone's opinion, that opinion is diminished in value, regardless of whether you are right or you are wrong.  This is not a sniping contest.  Disagree and respectfully converse about your differing thoughts, if you like.  Posts like the above, with attacks and criticisms, not about the post, but about the poster, are not educational, informative, or helpful.  They run counter to the manner in which ideas have been respectfully exchanged on the FF, IMO.  I do think that you have chosen an excellent screen name for yourself.  How about a little sunshine?  We would love to have you add to the conversation, without detracting from it.   Certainly, many of your former posts were contributory.  I'd like to continue along that line.  Just my opinion.  Doctorb

[Jeff]

I'd step in and say something but doctorb said it better than I would have.

[Dean186]

If you really don't know something that's OK, you don't have to make it up. You tried to get me into a debate on another post where I already knew you didn't know what you were copying and pasting, That's why I didn't bother to debate with you.

If I copy and paste something I will put it in quotes or make my references known.  I may use my old college books and/or the internet as a reference when I need them.   The only thing I copied and pasted in our past conversation was the power factor chart.  I never "make things up".

My writing skills have always been my weak point and it should be obvious that my post are my own words and not copied and pasted text from a technically publication or from the internet.  

Occasionally I will misspeak, like most of us, and then make a correction.  It's called conversation.

As far as presenting myself as an expert, I have never claimed to be an expert nor do I pretend to be one.   As far as understanding what I am trying to convey, I certainly do understand it, but I'm not always able to convey it in writing.  I received a Bachelor of Science degree in Electrical Engineering from Kansas State University in 1979 and did design work for General Dynamics on the F-16 fighter plane after graduating.  Like many with degrees, my career path changed and I have forgotten most of what I knew.  I however, still understand power factor and was pulling the information from retired brain cells and not the internet in our past conversation.  I find it best to never make assumptions about a person's background when conversing with them.  

Forums are educational and fun at the same time.    Gary has a camper running off grid using Trojan T-125 batteries and I have a camper with Trojan T-125 batteries and dry camp all the time.  The exchange of information is beneficial to us both.   His question was about battery life.  I gave him my best answer at the time.  If you don't agree with it, offer one of your own or ignore it.

I went over my old post and could not find where I might have offended you, but I must have since you decided to attack me personally on more than one occasion.  Whatever I may have said to offend you, I apologize.   If that is not acceptable, it might be better if you just ignore my posts.

I am not an expert, just another forum member with an opinion.

IMHO, FWIW, my 2 cents worth, etc, etc ...  Dean

[Dean186]

Gary, 

A book that I recommend to anyone that dry camps is:

Managing 12 Volts:  How to Upgrade, Operate, and Troubleshoot 12 Volt Electrical Systems [Paperback] by Harold Barre (Author)

You can find it on Amazon and here is the link.

http://www.amazon.com/Managing-12-Volts-Troubleshoot-Electrical/dp/0964738627/ref=sr_1_1?ie=UTF8&s=books&qid=1302364752&sr=8-1

[beenthere]

And we learn from your opinions as well as others
That's a fact!

[DarkBlack]

All right- maybe got in the sauce and struck a nerve.
Can we get a group hug? ;)

[Jeff]

I don't think so, but what we can do is give you a last chance to appreciate the atmosphere we strive to maintain on the Forestry Forum so you can follow that path from here on out.

[sharp edge]

Gary  If I could use your money  8) 8) I would go nucler= buy Ford Fusion hybrid and hook it up to the camper. They have a big battery and a big generater. Its 2011 now you are doing 2000.

SE

[Gary_C]

Well it was back to the camper for a few days and I watched the batteries closely. I deliberately let them discharge till the controller shut the inverter down and it was at about 194 amp-hours which seems OK. And the controller did shut down at 10.5 volts under load though the voltage rose to 11.2 volts as soon as the load was removed.

One thing I noticed is the inverter is fan cooled and through the winter that fan has not run as the inverter is in a storage compartment. But now the fan runs most of the time it is inverting or being charged. So that fan load is part of the reason for the seemingly faster discharge.

Another thing I noticed or rather was reminded of is two of the battery cables have corrosion under the crimped ends and that needs to be fixed. My son in law has a cable end crimper and I need to get some new ends and fix that.

So I guess I am satisfied for now on the battery life. It sure does take a lot of work and planning to live off the grid like this. You have to watch your power consumption and keep a close eye on the state of charge of your batteries all the time. 

[Dean186]

It sure does take a lot of work and planning to live off the grid like this. You have to watch your power consumption and keep a close eye on the state of charge of your batteries all the time. 

I agree Gary.  Have you replaced your incandescent bulbs with LEDs?  It sure does make a difference.  I replaced 8 bulbs in our camper with LEDs last year. 

[doctorb]

Happy Birthday, Dean!

[Gary_C]

  Have you replaced your incandescent bulbs with LEDs?  It sure does make a difference.  I replaced 8 bulbs in our camper with LEDs last year. 

No, and at the price I just saw of almost $20 each, I will probably not replace any time soon.

The one thing I have identified as being a power hog is the old non digital TV/Converter combination. I takes over 8 amps (measured on 12 volts) to run. Time to get a flat screen anyway, right?

I have a very small flat screen that takes less than 3 amps to run.

[Sprucegum]

Gary I have not used your particular brand of generator but some cold-weather gimmicks I have seen are;

Pink insulation tucked in around the carb or,

A flex pipe from the exhaust to the general carb area or,

An insulated box over the generator to keep the wind off. Might need an air intake though.

I had an English Ford car I had to take the carb in the house to thaw evry time it got cold  :  ???  : That's fun once or twice.......

[logwalker]

Gary. Did you say that you were running the 4 batteries as 2 separate banks. One thing to remember is that the amp hour rating is based on a 20 hour discharge rate and when you discharge faster than that the AH rating goes down dramatically. If you use the 4 as a single bank than the discharge rate will be effectively lower and will extend the run time.

I have run battery banks in several different situations and I always put some solar panels into the equation. Are you using any now?

And to address the shutoff voltage, 11.2v is almost flat and with a flooded cell battery you are doing damage each time you go that low. Consider AGM batteries if you don't have room for a larger bank. You can run them lower without damaging them as much. Pretty spendy batteries though.

Joe

[logwalker]

Sorry, I went back and read your initial post and saw you do use Solar. I think you would benefit from a battery bank twice as large. 6 batteries in a single bank would be the minimum I would try to get away with. Also angle you panels to the sun if you don't already do that. Should help a lot.

Joe

[mr T]

Ive had real good luck with Trojan Got 8 yrs out of my l16s Inow have 6 105RE charged by 3 kyocera 11o panels about 22 amp My batterys are in an enclosed box outside with a 2inch vent I ran a 4inch pipe to the box from heated cabin & installed a computer fan This helps keep them warm I keep my system above 12v & equalize every 30 days

[maple flats]

Try this link    http://www.trojanbattery.com/pdf/TRJN0109_TRJNUsersGuide.pdf   refer to pg 12.
It is Trojan Batteries chart for their batteries.
I am off grid and run my sugarhouse on solar/generator combined. You need some educating. Batteries have a maintenance routine that must be followed. Battery life is maximised by doing every thing 100% right. It was stated above that Trojan's should last 10 yrs. That is a very optimistic number. To even come close you would need to never use the power to under 80% SOC (state of charge). A typical life for Trojans properly maintained is 7 yrs but one can achieve longer sometimes but don't bank on it. If you would like a little lesson in battery usage and care, PM me, I will go over it with you.
To last the longest you must have a properly sized bank, have every control set perfectly, check PH and water level often and keep the terminals clean. You must also ensure the battery cables are in perfect condition, the entire length and at each connection.

[maple flats]

Do not equalize unless the SG's are more than .030 unbalanced or the fully charged battery SG is under 1.25. Your readings must be taken using a temperture compensated hydrometer. You can either use one designed to self compensate or use a standard hydrometer and do the compensation math. I believe the Trojan manual I linked has that info.These numbers are specifically for Trojan batteries, others may be different. Equalizing is not needed routinely. On my current battery bank (grossly undersized but used within it's limits to max discharge to 70% SOC.), the bank has only needed equalizing 1 time in 18 mos. Go by the numbers, do not equalize as a routine or you WILL shorten battery life. As I see it either you have incorrect info about your system or you are killing the batteries. Any battery drained to less than 50% SOC dies much faster. However, wait until this bank needs replacing. Then do an energy audit on your needs and get the proper bank. It is far better to use 60% as absolute lowest SOC, and even better to use 70% or better even 80%. Another thing that helps is testing properly. You should have isolator switches (to remove the charge and load from the batteries for the specified rest period for testing, I use 24 hrs but you can get fairly accurate readings if you just wait 8 hrs) Another test to determine the need for equalizing is to test  each rested battery, a difference of .3v from any one to the others also means to equalize. This method while it may seem better (easier) it is actually the last resort method.
You will do best if you download the manual and study it, then keep it for reference near your batteries. I set up a test sheet for my battery bank, I think I may have gotten it from the manual. If not look on Trojan Battery web site, it is there someplace. I test mine every week. If water (only use distilled water) is needed, only add to fully charged batteries unless the liquid is below the plates. In that case add only enough to cover the plates, fully charge and then bring the level up to barely below the split ring you see as you look into each cell. After topping off the water, put on charge again for at least 1 hr to mix the water into the acid mixture.
While I do not profess to be an expert, I do however use the same Trojan T125's and get good performance. Do not entertain the idea of adding more batteries to the bank now, batteries of different ages do not play well together. In fact when you buy your next set specify that you must get all batteries from the same lot #, even mixing different lots shortens the bank life, the poorer ones will bring the better ones down to the lower ones. It is not a mathematical averaging.

[jpgreen]

Gary, your problem is lack of sun and not enough panels to catch what little you have.  Not the batteries or controller, and would not be much of an issue with the cold if you had AMPS!

But 7.8 is your peak? Not gonna do it, and way to low....  :(  If you had 7.8 amps continous, then they would be doing well, and your controller would do it's job.

Your batteries are way undercharged and spend most of their life discharging.

If you had 20 amps hitting your batteries part time you would have more of a chance. Need more panels.

I got 9 years out of my Trojen L16's (12) in the house, and then replaced them with a new set and I have the old set working out in my shop. 12 YEARS on that set now. But, they are obviously not peak condition. I use them more like a capacitor and run my CNC machines with them.  Batteries will work (even old) if you have enough amps coming in for your needs.

[jpgreen]

After reading back-

Another note... Equalizing (over charging) is desulfating. It's boiling up your battery acids and removing the sulfates off of the plates. As your batteries sit in a state of discharge, the plates collect sulfates, which in turn shortens their life and amp hours.

So you need more amps, amps, amps!

Also like mentioned above- try not to discharge your batteries below 50%, and if you do, charge back up full pop as fast as possible.

Batteries charge much quicker and use less energy to bring them up when charging the top 50%.

Off gridding is a much different way of thinking than your truck batteries. You think- well if I get enough battery power capacity, I'll be OK.  WRONG!  .... 8)

With off grid systems, your primary concern is enough power coming in... AMPS! Batteries are a mere storage point.  Like a pitcher full of water. What you pour out (use), you have to refill. The refill is primary, and more important. Bleeding off power if you have to many amps is an easy luxury to deal with.

The opposite- not enough amps as in your instance causes numerous problems. And you are finding that one out...  8)

[maple flats]

I just reviewed the Trojan link I pasted above. I think your biggest issue is the temperature. The chart only goes down to 0 degrees F and the AH capacity at 0 is under 50%. You are going to -30. I think you need to find a way to keep the batteries warmer. This might pose a problem because venting is essential. Gassing is mainly at higher SOC so you might be able to restrict the vents slightly during use but open in recharge. I think you should contact the mfgr tech team of the batteries you are now using for their suggestions.
My guess is to shut down at a higher voltage or set the generator to start sooner. Does your system support auto start? As far as the blanket goes, ditch the elec blanket and get a real good sleeping bag, rated for colder than the temperatures you are dealing with.
Another point to realize is the voltage readings you are drawing to. The manual's SOC rates for voltage are for a battery at rest for 24 hrs, with a 6 hr minimum rest. They are not the shut off point in use voltages. You may have a hard time getting even 6hr resting readings. You might consider 2 battery banks and alternate use.
I also see a need for more solar. You say you have 50 watts. I have a 50 watt panel I use to recharge my 12 volt batteries ( 1= 12V takes 2 days to fully charge and I have a MPPT charge controller on it) but my system has 740 watts to charge a bank of 8 Trojan T 125's wired in series. You say you don't get enough sun and winter gets less time, but realize that PV solar gives the best charge at LOW temperatures. My 740 watt array is 240' away from my sugarhouse to be where they can get sun, and the panels are wired in series to reduce voltage drop. My 24V nominal panels wired in series give me 122-126 V when temps are at zero. I have not had -30 in several years. The only way you can run higher voltages to charge a lower voltage bank is with a MPPT controller. I use a FX80 which is rated at 80 amps on 12,24,36,48,and 60 volts. It will shut down if infeed volts reach 150. That is why I only wire 4 and not 5 in series. I want the energy and can't afford to have shutdown on over voltage safety. Another point, my array is too small. I am adding 4 more this year and another 4 each year until I get to where I need it. My battery bank is also too small, but I will use the 8 t-125's until they need replacing and then I will get a much larger bank.
If you add a panel, get exactly what you now have, different panels do not play well together. If you move your panel(s) farther away be sure to use the right cable gauge to bring power to the camper.

[SPIKER]

I wanted to post some information regarding battery & battery deep cycle issues.

One thing I have found helpful is to use anti-sulphate chemical in them.   There are several brands available and they work well.   I use it in my tractor battery and has kept my china battery alive at near 10 years now with at least 4 major discharge errors by leaving keys on or other problems.

this is a pretty good site here
http://www.discountbatteryco.com/pages/batSTORAGE.html#

some more info http://batterydoctorsoftampabay.com/technical_info

more

http://batteryuniversity.com/learn/article/how_to_restore_and_prolong_lead_acid_batteries


anyhow have fun do a search for "battery anti sulphate chemicals"
or  "battery anti sulphate pulse chargers"

I used a chemical called "Charge-It" as a battery anti sulphate chemical treatment 2 years after loading up my CHINA battery with acid as it was shipped dry.   the Key was on and the battery voltage was 4.5 volts give or take. I hit it with a re-charge "boost 200 amps 15 min, high charge 50 amps 4 hrs and overnight 2amp pulsed trickle charge."   checked acid which was a bit light topped with a acid D.I. water 50% mix and has held 13.5V pretty good going on 10 years old.
   It keeps a pulsed maintainer on-off of it regularly as well just cause it only is used maybe 4 hrs in 3 weeks with 1 or 2 start/stop cycles.

mark

[twomules]

I spent eight years designing chargers and instrumentation for motive batteries, lift trucks, buses, wheelchairs and tanks and still find these vile boxes of noxious chemicals perplexing.

If you find ice in the battery it's not fully charged.  A fully charged battery freezes around -74F.  At 50% charge it freezes around 5F, at 0% charge it freezes around 18F.  Batteries have a lot of thermal mass if you keep them fully charged when idle they won't freeze.  At any reasonable temperarure.  I live in Wisconsin so reasonable is on the cold side.  If they must sit partially charged for long periods (a bad idea) then insulation or even a heater may be necessary.

The sulfuric acid is turning into water as the battery is discharged and the lead plates are converted into lead sulfate.  This is normal and not harmful, it's how the battery works.
Charging the battery converts the lead sulfate into lead and the acid increases in strength. 

The sulfate on the plates is at first porous and reversible but the crystals grow becoming a nonporous insulating mass which is difficult to reverse.  If the crystals grow too big they mechanically damage the plates and then the battery is not recoverable.  A second reason to keep the battery fully charged is corrosion.  Plate and inter-cell connection corrosion is increased when the battery is not fully charged.

I tested many types of desulfators in the laboratory.  The best desulfator is gently charging and discharging the battery.  Full charge, slowly then discharge to 20%
slowly, repeat as necessary.  At the point when the battery is looking better an equalization charge would probably be a good idea.

Large batteries benefit from having the electrolyte stirred.  Some batteries have an air stone like those used in fish tanks built in and compressed air stirs the electrolyte.  Pulse charging and pulsed discharge during charge sometimes claim the benifits of stirred electrolyte but I couldn't verify them in the laboratory.  In fact I couldn't veryify any benefit from them.  I tried pounding on the steel case of a 4000lb battery with a mallet to see if shaking bubbles off the plates had any effect.  Didn't seem to.  Maybe I didn't use a big enough mallet. 

Determining the depth of discharge by measuring the voltage under load depends on the discharge rate and the temperature.  If you measure open circuit voltage the battery has to rest first and it still depends on temperature.  If the battery management system doesn't have a temperature sensor so it can compensate the measurements it will be inaccurate.  Here is a good article on SOC measurement
http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

Even with temperature compensation, checking the computed state of charge by measuring the cells specific gravity (temperature compensated of course) is a very good idea.  These guys sell a nice hydrometer http://www.freasglass.com/battery.htm

I guess I'm rambling now, eh?  Keep an eye on the specific gravity, don't discharge the battery past 20%.  Charge it to 100% as soon as possible especially in cold weather.
Remember that 100% includes a "topping" charge.  How much is that?  Stop just short of when the battery boils as it does during equalization charging.

Good luck!

[Sprucegum]

Twomules;
          Thank you for sharing - that's good stuff to know.

[mad murdock]

Welcome to the Forum Twomules!  great information on a very overlooked item, the battery.  We deal with them constantly, as we depend on them to start expensive turbine engines, and not fail in the middle of a start.

[DouginUtah]

Is there some rule of thumb which says how fast a fully-charged 12 V. battery looses its charge when not being used?

The reason I ask is because I don't know how often I should put the charger on my teardrop battery during the winter.

Does it occur faster the colder it is?

[twomules]

It depends on the battery and the installation.  Even small loads connected to the battery like engine control modules and clocks make a huge difference.  It's best determined by experimentation.

Keeping the surface of the battery around the terminals clean and the battery disconnected from everything, I connect the charger every three months over winter.  That works for my old tractor but ymmv.  If it's difficult to reach the battery terminals a disconnect switch may be a good idea.

Cold slows self-discharge down because it depresses the voltage.  It also reduces capacity so it may appear that the cold is discharging the battery. 

Main thing, keep enough charge on the battery so it won't freeze.  Not only can it ruin the battery by buckling the plates but it can crack the case.   Then all the acid pours out when it thaws.  Yes, I've done this.  Didn't do the motorcycle much good.

[DouginUtah]

Thanks for the reply, twomules.

I've been charging it about every two months, and the coldest it got here this year was -5°F.

[maple flats]

Gary C, I do not use batteries off grid, but I do know a bit about battery construction, and what factors effect battery service life, etc.  As has been aptly stated, close monitoring of discharge state, and not letting batteries get below a certain level will have a great effect on what usable life one gets out of a battery.  Another thing is battery construction itself.  I am speaking from my experience with 25+ years of aviation maintenance and operation background here.  The best batteries (as far as capacity, discharge/recharge cycle life, and overall performance have plate material that is very pure, and the real expensive batteries will have plates made from solid lead plates, rather than the lead powder pressed plates, with the mesh composite construction.  The solid plates are less susceptible to sulfidation issues, and have a much higher cycle life, the downside is that these type of batteries typically are quite expensive to build, and to buy.  This may or may not be of help to you.  The heavy industrial type batteries make excellent choices for aux. or off grid power systems.  In my area, if a guy can find the telecom batteries that the phone companies discard usually every 2 years, are good to build a system around, as the cells are HUGE, and you can string whatever you want for your system in 1 cell (2 volt) increments.  One of those cells (2 volts) weighs about 40 lbs, they have a ton of capacity, and good cycle life.

mad murdock, how would these 2V cells be listed in Google. I tried every way I could think of and get nothing. Seems someone one the web will be selling them if they exist. Do you know if they are Rolls Surrette batteries? They are the only on I am familiar with that come in 2V. There may be many more out there but I have not seen them.

[maple flats]

In my area, if a guy can find the telecom batteries that the phone companies discard usually every 2 years, are good to build a system around, as the cells are HUGE, and you can string whatever you want for your system in 1 cell (2 volt) increments.  One of those cells (2 volts) weighs about 40 lbs, they have a ton of capacity, and good cycle life.

Mad Murdock, Do you have any idea how these might be listed on Google or other search engine. Or what excatly are the batteries removed from service by telcom companies?

[mad murdock]

I've not tried to google them, they are used by phone companies to supply system voltage at all times in case of power grid failure, (tht is why your phone works, if it is not a fancy wireless phone, when the power is out).  You could contact the local phone co, or someone that is a tech for them if you know one.  Trojan makes a 1110Ah battery that is 2V and weighs 116 lbs, along the lines of the ones I mentioned.  a bank of those would give a guy lots of power, and they have a 5 yr warranty.  Model # L16RE-2V .  That is the best I can do for you right now.  They have these on ebay and other sites as well.