I keep my trailer in a storage lot that does not provide electricity. I keep the battery disconnect switch in the off position. I will measure the voltage on the batteries and for example will show 12.5 volts. Go back two weeks later and they measure 12.4. Is this normal or do I have something drawing a little on the batteries.Don

Deep cycle batteries self discharge at some place around 5% to 20% per month, more for those reaching the end of their life. The only way to find if you have a vampire load is use an ammeter and the way to assure you do not, is to disconnect the negative terminal from the battery.

The condition you see is normal but you have to do something about it. Batteries should be on "disconnect" to lessen discharge from phantom loads. The self discharge rate mentioned is more for 12v batteries than 6v batteries.The batteries should be recharged at least by the time they get to 12.2 volts (60%). It would be better to do it at least every other month during storage to keep sulfation from occurring on batteries below full charge.Better yet, get a solar-panel of at least 10 watts to keep fully charged (12.6+v) battery(s). A larger panel would be needed to help recharge batteries with some discharge.When we owned a trailer I normally removed the batteries and stored and checked them at home.

Use a test light and see if the disconnect is really disconnecting, I suspect it isn't. Others have had similar issues, check the wiring.

Hi,It has nothing to do with voltage and everything to do with the chemistry of the battery. Most six volt batteries in use by RV folks have high antimony content and may self discharge at up to 1% per day.A modest solar system would be a good way to keep the batteries in tip top shape between trips.MNtundraRet wrote: The self discharge rate mentioned is more for 12v batteries than 6v batteries.The batteries should be recharged at least by the time they get to 12.2 volts (60%). It would be better to do it at least every other month during storage to keep sulfation from occurring on batteries below full charge.Better yet, get a solar-panel of at least 10 watts to keep fully charged (12.6+v) battery(s). A larger panel would be needed to help recharge batteries with some discharge.

pianotuna wrote:Hi,It has nothing to do with voltage and everything to do with the chemistry of the battery. Most six volt batteries in use by RV folks have high antimony content and may self discharge at up to 1% per day.A modest solar system would be a good way to keep the batteries in tip top shape between trips.This but with new 6V's it's more likely 1% per week. 12V batteries would be around 2-3% per month.

Battery Parasite Draw or Normal | Good Sam Community

21 Replies

MEXICOWANDERER
Explorer
Mar 27, 2014
Trade your "old" good one to somebody that can use it. A trade-in is a trade-in. Not everyone can afford new batteries. Recycling something perfectly good is a crime of resources IMHO. Help someone less fortunate out :)
Duck
Explorer
Mar 27, 2014
Wanted to post back to the solution to my problem. Took both batteries out and took them home for charging. What I found out is that one of the batteries had a bad cell and was drawing down the other battery also. Charged the good battery to full charge and let it sit for two days to get rid of the surface charge. Held 12.75 for the remainder of the week. Before we leave on a trip will go ahead and replace both since the good one is 2 yrs old.
Almot
Explorer III
Jan 24, 2014
10w per 450 Ah of 4 GC, yes.
5w per 225 Ah of 2 GC.

More watts is needed if batts are older, and more watts if ambient temps are high. Again, more watts if the location is not too sunny.

2.5W worked fine for 50AH very old and very poor condition (= fast self-discharge) starter batt in winter at latitude 27, though mostly sunny. I figure the self-discharge of that battery was 2-3 times higher than usual, i.e. 2.5w would work for a normal 100 Ah batt.

Up to 20w I wouldn't bother with controller.
pianotuna
Nomad III
Jan 24, 2014
Hi,

12.5 watts per 100 amp-hours works in (sunny) Saskatchewan.
time2roll
Nomad
Jan 24, 2014
Almot wrote:
smkettner wrote:
Skip the 5w solar and get a real panel of 50 to 120 watts and controller...

What else would he suggest, having his 700W solar on the roof ;) ...

Seriously though, 5W will do, for a pair of GC flooded batts or an equivalent 225 AH 12V bank, up to say, 250 AH bank. 5W panel generates very low current so the controller is unnecessary. This is usually the simplest and the cheapest solution. A 50W panel with controller would've been better, but is not absolutely necessary for a bank of that size, and they start from ~$120.

I did 15w into 4x GC2 for a couple years. Woefully inadequate even in sunny Southern CA. Batteries were otherwise completely disconnected. 10w per battery would be absolute minimum IMO.
MEXICOWANDERER
Explorer
Jan 24, 2014
Mr Duck, if it is feasible try to charge the batteries thoroughly before storage. At a rate of 5 amperes per 12 volt battery until voltage reaches 15.0 volts then stop the charge, disconnect the battery and then monitor static voltage once a month.
Almot
Explorer III
Jan 24, 2014
smkettner wrote:
Skip the 5w solar and get a real panel of 50 to 120 watts and controller...

What else would he suggest, having his 700W solar on the roof ;) ...

Seriously though, 5W will do, for a pair of GC flooded batts or an equivalent 225 AH 12V bank, up to say, 250 AH bank. 5W panel generates very low current so the controller is unnecessary. This is usually the simplest and the cheapest solution. A 50W panel with controller would've been better, but is not absolutely necessary for a bank of that size, and they start from ~$120.
time2roll
Nomad
Jan 24, 2014
Skip the 5w solar and get a real panel of 50 to 120 watts and controller.
Your batteries will last twice as long compared to the current situation.
Duck
Explorer
Jan 24, 2014
Appreciate all of the replies. Learned more then I knew before.
Don
Almot
Explorer III
Jan 24, 2014
Drop 0.1V in 2 weeks is a little high, but still in the ballpark for flooded batteries. It's called self-discharge. Leave them for 3-4 months and they will discharge by 50% or more. The warmer is temperature, the faster they self-discharge.

Get a small 2.5-5.0 watt solar panel from Amazon or a local autoparts store - those that have a wire with clamps and/or cig lighter plug attached. You clamp it to the battery terminals and it does the job. They are not very cheap, $30-50 bucks, but cheaper than a new battery.