What is Eating Those Batteries?

I went to Quartzite yesterday to visit an old friend who is dry-camping on BLM land and has been having some electrical problems with his travel trailer, a 2001 KZ model. The problem is that even with 2 new 12V Group 29 Marine/RV batteries (Walmart), he will go from fully charged one afternoon to 12.05 volts by the end of breakfast the next morning.

I should tell you that this guy is a very experienced RVer who has dry camped a lot and understands what he needs to do to conserve battery, but this has him stumped. He uses one light, sometimes 2, in the evening for a couple of hours; listens to his 12V stereo for an hour or so, runs the heater in the morning for about an hour, water pump as needed charges his cell phone. Couldn't be that hard to figure out, right? Has to be that there is a parasitic load draining the battery, or that some appliance is pulling lots of amps, way more than it should be. So we got out the electrical tester and checked for parasitic load. Results were 25 milliamps, everything off that can be turned off. No parasitic load, at least not while we were testing.

So, if the problem isn't a parasitic load, it must be that something is pulling lots of amps while it is running. I decided that the easiest and most rational way to test was to pull the 12V fuses, one by one, and see what appliances were on a given circuit and to determine how many amps they were pulling while in actual use. Sure enough, nothing turned up as unusual. The item that pulled the most amps was the furnace, and that was 5 amps, just about what it should be. All other items were exactly what you would expect. I don't have the complete list to publish here, but absolutely nothing jumped out as being unusual.

So if no parasitic load, and nothing is pulling more amps that what you would expect, what is eating the battery? And how do you go about systematically testing to find out what it is? The trailer does have some age, and my suspicion - backed by absolutely nothing - is that it's the converter/charger. But why would that cause a large discharge from the batteries? I don't have any idea.

Any suggestions? Any help? Anyone have a similar problem who has solved it and willing to share their knowledge?

80 Replies

NinerBikes
Explorer
Feb 01, 2014
I think he has a charge controller issue in his motor home. It is not putting out a high enough voltage, maybe stuck in maintenance mode at 13.6 V. Have your buddy measure the voltage at the battery posts while on the shore power charger. At start up and after 5 or 6 hours of charging. The voltage should rise considerably.

You should be able to get that battery up to 1.270 -1.275 or higher for specific gravity when fully charged. Also sounds like he does not have enough solar panel and charge controller with adjustable voltage settings to get the job done properly, he probably needs another 120-200 watts on top of his 100 watt panel. General rule of thumb is 1 watt per amp of battery capacity, and you would need more with the long nights in the winter, and short daylight hours for charging and low angle of sun to get things fully topped off. 300 watts of solar panel for 2 x 110 amps for battery should help get things up there when it's winter time and the nights are a lot longer. Portable, and he should be aiming them at the sun 2 to 3x a day to maximize amps yielded for recharging.
NinerBikes
Explorer
Feb 01, 2014
double post
BFL13
Explorer II
Feb 01, 2014
He seems to be using a pulse type desulfation method, which does not raise the battery voltage. He needs to charge the batteries to about 15v or so and do a desulfation that way.

Solar direct will get the voltage high enough if there is enough time in daylight. It won't go to 18v. It just climbs from what it is now to whatever he lets it get to (got to keep track) He should get it into the 15v range and let it bubble for a while, taking SG spot checks. When SG stops rising, or the battery gets too hot, he should stop.

If he can't get there by sundown then just leave it and restart next day to go the rest of the way, ASSuming the battery is disconnected overnight so it won't fall back overnight.
Ron_Nielson
Explorer
Feb 01, 2014
To update the posting, my friend had moved to a site where he has 110 power and has been charging one of his batteries on the de-sulfate mode of his battery charger for about 2 1/2 days not. His SG has increased very little. One thought is that he should attach his newly acquired solar panel to the battery to enhance the process. Here's his message to me:

Good Saturday morning to you. I have been desulfurizing my battery for 61 hrs and I'm not getting anywhere fast enough. All 6 cells were right around 1.200 SG. So I'm thinking about connecting my solar panel direct to my battery and charge it all day and see what happens at the end of the day.
Questions: will this charging increase my SG? Will the 18.5 volts hurt the battery anymore than it's already been damaged? Would you have any concerns? I will continue running the desulfurization of the battery at the same time. Thanks

Since battery has been charging for a considerable time with little progress on increasing the SG, does that mean the battery is shot? Or is there still hope for it to come back? If so, what are the next steps?
big_buford
Explorer
Jan 28, 2014
In your first post you said 25 ma parasitic load. If there is no load on the batteries what else could it be but batteries?
BFL13
Explorer II
Jan 28, 2014
If they have not been brought to 100% after a week or two of camping off grid doing 50-90s, you could see that. I get "progressive capacity loss" from doing just three 50-90s in a row where each time it gets worse, and the SG gets very low even though the voltages stand up ok.

You can tell the capacity is lost from how fast it takes to discharge or recharge the 50-90. That 40% in AH becomes smaller and smaller.

You just have to find shore power and get back to 100 so you can start over off grid or else you need enough solar to get to 100. That can be tough in the daylight time so I do a split bank thing and do one battery at a time on solar leaving it disconnected overnight so I can start again in the morning and get it to full on the second day. Meanwhile you run the rig on the other half of the bank. Then swap over so it can take four days to do two batteries. PITA.

The solar needs to be with no controller so the voltage gets right up to desulfation speed for that to work best or you might never get the batts done in the available daytimes. Easier to go to a full hookup park for a day if not going home anytime soon.
Ron_Nielson
Explorer
Jan 28, 2014
Here is some additional information:

Yes, I'm reading the postings. I don't think it's sulfated batteries. They said the same things last summer. Tomorrow I'll get another new group 29 marine battery and install the 100 watt solar panel. At this point, I don't think 100 watts can keep up with the battery loss. Keep in mind, I'm no longer using any 12 volt stuff in the trailer. Only one light. No heater, no stereo, charging the computer and phone in the car. Nothing but one light and water pump. That's it. Something is draining those batteries and we can't find it.

As you can see, he has ordered a solar panel to help keep his batteries charged. Looks like it has arrived or will arrive soon.

Sure is frustrating. Only 1 light in the evenings, water pump runs infrequently, and batteries are being drained. Can the problem really be because of sulfation??
MEXICOWANDERER
Explorer
Jan 28, 2014
Buy a battery, Charge it 101%, discharge it. Let it sit 4 weeks. Ya gotcha a block of wood. Said it before on this forum, batteries are like wimmen, you ignore them and you are in deep. I mean r-e-a-l-l-y d-e-e-p.
BFL13
Explorer II
Jan 28, 2014
Those batteries are only three months old. Hard to believe they are that badly sulfated. How did that happen? Wonder if they/that one was ever fully charged when bought.

Look down the six cap holes with a flashlight. Are half the cells covered with white and the other three brown (alternating in a row)? That's badly sulfated

The dates (month is a letter, year is a number)on the battery are
-build date stamped on side of plastic case near the top (need flashlight to read it)
-some have a build date in one of the lead posts
-date "last charged" sticker on top with perhaps also the date due for next recharge
-purchase date sticker with yr/mo holes punched

Compare actual build date with last charged sticker date.

You will need shore power or solar to recharge /desulfate the battery. It would take me a couple of days at least of "nursing" not just one eight hour session but I don't have Mex's calibrated equipment.
mena661
Explorer
Jan 28, 2014
Doesn't look like a shorted cell but there's definitely some sulfation going on. You might be able to recover these batteries to a working state but there is some permanent damage. How much? Who knows. You need to put them on a separate charger till it registers full then on another charger that has an equalize function.

EDIT: Or just do what MEX says. :)

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What is Eating Those Batteries?

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