I just went out to the TT to start getting it ready for our next camping adventure. Currently it only has the original Interstate Group 24 Marine battery on it (the Deka's and Unisolars seem to be enjoying hanging out at the house).To maintain it, I just put the solar 5w square on it, partially obstructed by shadow. It seems to briefly hit a high of about 13.7v in the peak sun (a little high?). I took the square off a month ago so just now I got a chance to measure the one month resting voltage. 12.90v after 30 days. The battery seems happy. Seems like incredibly low self discharge for a flooded battery. Too much overcharging, or just enough to keep sulphation to a minimum?My older batteries are more like 12.6-12.8 24 hour resting voltage.Jim

I would put a load on the battery for about 5 minutes, and recheck the voltage.A surface charge would disappear. The same reading means your meter is reading high. I would replace the meter, or at least the meter's battery. If it's still 12.90 volts, get a better meter.By the way, if you remember back in March we were discussing upper limits of voltage for charging batteries under different temperatures. My Schumacher SC-12000A Speed Charger reached 16.1 volts while finish charging between 90% and 100% (full cutoff) when charging @35F ambient temperature.Last week I got chances to recharge the battery twice. The first time the charger reached 15.7 volts after 90% @ 65F ambient temperature. The second time the charger reached 15.3 volts after 90% @ 82F ambient temperature.While the charger does not have a thermistor to read temperature, it does use programing to limit the maximum force (voltage) output to keep the battery from over-heating (per the manual).Mark B.

It is a decent but not great meter. An Amprobe AM240 with auto off to conserve battery. It agrees to within 3/100ths of a volt with 2 turnigy and 2 watts up meters. The odds of a surface charge after a month are pretty much 0 I think.Jim

At any rate, don't count on the suspect reading of 12.9 volts to add up to any more minutes of useful time.

Brand new battery maintained by a low max volt low power solar panel to avoid sulfation having a resting voltage of 12.9 if ambient temperature is high seems reasonable. My boat batteries disconnected for 3 months in winter typically still read 12.8 when put back in service. They are maintained by a small solar system during the season (30 watt with morningstar sunsaver) but disconnected for winter storage

Interesting point. Around 90 degrees out and the battery box was in the sun when I measured it. That's one of the reasons I cannot bring myself to mount the Deka AGMs on the TT yet. Parking spot faces south and it seems wrong to leave them there to cook.Jim

5w 15v solar maintainer | Good Sam Community

15 Replies

64thunderbolt
Explorer II
Jun 20, 2013
Come to Phx if you want to watch batteries bake. Our overnight lows are in the mid to high 80's right now and will get warmer as summer progresses. If we get over 3 yrs out of our truck batt we are lucky. I got 6 yrs out of 2 grp 27's in my toyhauler with a lot of TLC.
pianotuna
Nomad III
Jun 20, 2013
Hi,

You can never get back what shales off the positive plates.
HiTech
Explorer
Jun 20, 2013
In Michigan I never gave it a thought. Gulf Coast climate and Texas sun have caused me to rethink that.

Jim
mena661
Explorer
Jun 20, 2013
pianotuna wrote:
Hi Jim,

I think you mean over 25 c (77 f)

Conversely as temperatures drops life span increases.

It's all do to the speed of the reaction. The higher the temps the faster they happen.
Yep, you and Jim are exactly right. I had forgotten about that. Probably because you get some battery life back as temps decrease.
HiTech
Explorer
Jun 20, 2013
Yes exactly.

Jim
pianotuna
Nomad III
Jun 20, 2013
Hi Jim,

I think you mean over 25 c (77 f)

Conversely as temperatures drops life span increases.

It's all do to the speed of the reaction. The higher the temps the faster they happen.
HiTech
Explorer
Jun 20, 2013
I should pull the info i found back up but temperatures above 77 have a big effect on battery life. It is some dramatic drop for every 10 degrees C above 77.

Measuring the 2 year old group 27 Duralast marine deep cycle, it is only 12.77 v after sitting less than a week. I had the solar square on it for a month but in a location with only maybe 2 hours a day of direct sunlight. This battery has spent it's life on a maintenance float charger running a gate, but I don't think it ever had to function in a power outage as it is designed.

Quite a difference in resting voltages between it and the newish group 24 Interstate.

Jim
mena661
Explorer
Jun 19, 2013
I don't think the temperature is an issue unless your float voltage is too high. Batteries are not going to gas just sitting there. You might get some deformation of the casing but probably not at 90F. I'd just keep them out of direct sunlight (ie inside a box)
HiTech
Explorer
Jun 19, 2013
My thoughts too. Maybe a solar panel!

Jim
pianotuna
Nomad III
Jun 19, 2013
Hi,

Put the square back on. 13.7 is just fine.

How about a sun shade for the Deka's?

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5w 15v solar maintainer

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