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Old 01-18-2015, 04:08 PM   #1
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2014 27' FB International
Avila Beach , California
Join Date: Nov 2014
Posts: 63
Battery discharge question


We have a 2014 27ft fb International with a 100w solar panel that will bring up two newly replaced group 24s to 12.5v according to the See-Level monitor by the end of a sunny day. However by the next morning the monitor normally reads in the mid to high 11s, e.g. 11.5-11.9.

When the batteries were replaced under warranty the dealer allegedly checked for shorts that would draw down the batteries and found none, and attributed the dead batteries to simply being bad, old or??? We have the normal power-suckers, CO2 monitor, fridge, in addition to a power awning with a "brain" that is drawing power whenever the rig is in the "use" mode. We are very conservative and do not run the furnace at night, turn off the water pump, sound system's main power, and burn no lights.

Given we have read that one should not allow the batteries to discharge more than 50% for fear of ruining the batteries (some say 40%), and considering the conversion table that has been posted to the forums says a battery reading 11.75 is at 30% state of charge, do we have a problem, or may I be reading the table incorrectly?


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Old 01-18-2015, 05:52 PM   #2
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Naples, FL , Hood River, OR
Join Date: Dec 2005
Posts: 7,354
Actually, full batteries are NOT 12.5VDC, but more like 12.8VDC and 50% depth of discharge is 12.2VDC (some folks list 12.7VDC as 100% and 12.1VDC as 50% for liquid lead acid batteries). Your batteries are never reaching full charge of the only get to 12.5VDC, and may not be retaining sufficient charge if the regularly discharge to 11.5-11.9VDC on a daily basis.

You should have your batteries checked for charge retention once they have been properly charged to FULL, not to 12.5 VDC. You also might benefit from a total trailer disconnect switch that will remove the battery power completely from the trailer's electrical system.
Lew Farber...ABYC Certified Master Marine Electrician...RVIA Certified Master Tech ...AM Solar Authorized Installation Center...AIRSTREAM Solar & Electrical Specialist...Micro Air 'Easy Start' Sales and Installations
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