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Really, It Was Not My Fault...........

Really, It Was Not My Fault...........

I immediately went to the barn and grabbed my DVM totally figuring this battery was a goner. It tested with an open circuit voltage aof 12.54V! This after sitting in a freezing cold then blistering hot shed throughout an entire Maine winter and summer.

I was a total disbeliever at the resting OCV of a flooded battery that has sat 100% uncharged for nearly 9 months. I grabbed my refractometer and performed specific gravity checks on each cell. They all agreed and all agreed with the DVM at the SOC..

So this causes one to wonder why there is all the concern around self discharge? I have to assume that nearly 20-30 days of this summer saw the shed temps well over 110F. The shed is not insulated and has a black asphalt roof. If we are to believe OCV (open circuit voltage) and SG readings (specific gravity) it puts this battery at approx 90% SOC after at least 9 months of sitting there un-charged.

Interesting n=1 data, to say the least......

OK off to charge and equalize this battery... Face palm.............

EDIT 10-28-13: I finally got a chance to perform an equalization, a few deep cycles to 11.7V then full recharges, and then conducted a 20 hour capacity test on this battery. It completed the test with 78.8% of the 20 hour rated capacity.

If you were paying attention early on in this article, this 5 year old battery had previously tested at 79.4% of rated Ah capacity. After sitting for nine months, through a full winter and then a hot summer in my shed, the battery lost only 0.6% of its previous tested Ah capacity. My suspicion is that if I had tested it in April I would have seen minimal to no loss and the summer heat is what really caused this minor loss of capacity.

Considering this battery sat uncharged & untouched through an entire winter and an entire Maine summer I find that pretty darn amazing. I have no explanation for how the summer heat in that shed did not destroy this battery? I would have thought the stratification alone would have murdered it but perhaps the winter hibernation also perhaps inhibits the negative effects of stratification too..

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Eric Grina 12-Oct-2016 17:10
I've had similar experience over 7 years of life on 2 Group 31 AGM's, normally wintering without charging with little self discharge. Last winter for the first time I left a 30 Watt solar panel sitting in the cockpit under white shrink wrap boat cover and connected to the batteries. To my amazement the panel still had significant output. Would you feel there is a danger in this practice as you feel (and I agree) there is with leaving a 110V battery charger connected?
Guest 26-Oct-2014 00:38
i am in Halifax NS. I am leaving my batteries on board this year, first time. Was unsure until I read this article but feel much more certain as I have bank of three to worry about (large Surettes, great batteries except for the weight). Will follow what you have done, ths for the test and info.