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Compass Marine How To | all galleries >> Welcome To MarineHowTo.com >> Effect of Winter on Battery Self Discharge > Really, It Was Not My Fault...........
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Really, It Was Not My Fault...........
09-SEP-2013

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 over 100F. It is uninsulated with a black roof... If we are to believe OCV and SG readings it puts this battery at approx 90% SOC after at least 9 months..


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 and then conducted a 20 hour capacity test on this battery. It completed the test with 87.4% of the 20 hour rated capacity. The rated Ah capacity is 125Ah and I got 109.25Ah's out of the battery at a 6.25A load before it hit 10.5V at 80F.

If you were paying attention early on in this article the battery had previously tested at 112Ah. After sitting for nine months through a full winter and then a hot summer in my shed, the battery lost only 2.75 Ah of tested 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 through the stratification alone would have murdered it but perhaps the winter hibernation also inhibits the effects of stratification too?


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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.