On Wednesday, January 25, 2017 at 3:22:11 PM UTC-8, Charlie M. (UH & 002 owner/pilot) wrote:
Heat dried the battery out, pretty simple. Batteries should be stored in cool temps, that does more for life than state of charge although that also has a bearing.

Yes this is very likely exactly what happened. really hight temperatures cause the electrolyte to evaporate out the vents. Nobody really thought "sealed lead acid" was really sealed did they? The more correct name is VRLA or Valve Regulated Lead Acid... the neoprene valve that opens when the battery gets hot and the electrolyte evaporates out of. Which is why you want to not charge at high temp, and always charge with he battery upright so it does not blow extra electrolyte out the vent. There is such a small amount of electrolyte wetting the mat between plates you don't have a lot to start with. If you are keeping batteries at high temperatures is more likely what causes problems than sulfating issues.

And a VRLA battery discharges nowhere near ~1% per day, it more like a few percent per month in good storage conditions. Yes it increases at high temps. The ~1% per day is for old style flooded lead acid batteries. (incidentally a way I've seen folks destroy VRLA batteries is leave them on incorrect chargers over winter thinking they need to do that to avoid self-discharge issues. Nope. The incorrect chargers can just evaporate away all the electrolyte. If you are not sure you have a specific VRLA charger correctly sized to the battery that will enter float charge mode properly then just charge the battery, disconnect the charger and then recharge again at the start of the season.