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12V battery overcharged?

Thread starter #1
About 8 years ago I mounted a small 4W solar panel to my shed to keep the 12V flooded lead acid battery charged on my infrequently used tractor. The solar panel has worked great without any problems. I just replaced the tractor's 10 year old battery with one with more cold cranking amps for the upcoming winter. The old battery has been out of the tractor for about a month and it still reads 13.1 volts. I know a fully charged battery should be about 12.6V. Why is this old battery so high? Have I been overcharging all these years? I thought I did not need a charge controller when using any small panel less than 5W. Is that true? Further research suggests 2w or less for each 50 battery amp-hours is fine without a controller and a typical small start battery is only 45 Ah so perhaps I have been overcharging. Any suggestions?
 

tcmtech

Banned
Most Helpful Member
#2
More than likely it electrolyzed enough of the water out of the cells to push the acid concentration up while at the same time over conditioning the plates thus giving you the higher than typical open circuit voltage reading.

Odds are if you added distilled water and ran the battery down hard then recharged it a few time the open circuit voltage would come back down.
 
#3
More than likely it electrolyzed enough of the water
R_C Have you been topping off the battery with distilled water ?
Did it still work in the tractor before you replaced it?
I did the same with a battery for my seldom used truck.
the battery was 12 years old when I sold the truck and was still working good In the Arizona desert heat.
 

JLNY

Active Member
#4
The nominal voltage of a lead acid battery varies quite a bit with charge level, chemical concentrations, temperature, and load conditions. Charging voltages of 13.8-14.4V are not uncommon. I would say a nominal voltage of 13.1V is nothing to worry about. Lead acid batteries are very robust and not nearly as sensitive to overcharging as something like a lithium battery.
 
Thread starter #5
More than likely it electrolyzed enough of the water out of the cells to push the acid concentration up while at the same time over conditioning the plates thus giving you the higher than typical open circuit voltage reading.

Odds are if you added distilled water and ran the battery down hard then recharged it a few time the open circuit voltage would come back down.
I did not expect the higher open circuit voltage but this makes sense. Before removal the battery was still starting the tractor without problem but it had been a long time since I topped off with distilled water. I just checked and the tops of the plates in each cell were exposed and it took about a pint and a half total to bring all cells up to the full mark. Immediately after filling the open circuit voltage dropped a tenth of a volt so that appears to confirm your diagnosis. I'll add a load then recharge to test. Thanks.
 

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