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Old 06-26-2013, 10:00 AM   #4
Underway
Guru
 
Join Date: Aug 2012
Posts: 741
Quote:
Originally Posted by ksanders View Post
What do you mean "bad cell"???

From your description there is nothing wrong with your battery bank.

Bag your troubleshooting and enjoy your boat. 12.4 volts out of a 12 volt system is just fine!

Here's how lead acid batteries really work on boats.

Your charger will end up while on shore power "floating" your battery bank at somewhere between 13.1 and 13.5 volts. Opinions vary as to the best float voltage but anything in that range will work just fine.

Once you remove shore power the normal loads on your boat will draw current from your batteries. Boats all vary as to the actual loads, but even the smallest cruiser has at least a fridge on all the time.

Your battery voltage will go down and stabilize at 12.0 volts. It will stay at 12.0 volts give or take during much of the discharge cycle.

As the batteries are depleted they will eventually go down in voltage somewhat depending on how deeply you discharge them prior to re-charging.

There is a battery myth floating around here to read the "at rest" voltage of your bank to judge its health and or charge. While that method might be OK for a set of batteries with no load, it is not applicable to a marine house bank, bacause a house bank does not sit "at rest". Even if you removed all loads from your house bank the "at rest" voltage method is not all that good.
Guess I thought there was an issue because the bank used to settle at 12.6 with everything off. The house bank has been in float mode on the three stage charger for a couple of weeks. I did have the big panel switch set on "off" before the "at rest" period, and the fridge was running on AC. For some reason I thought a weak cell in one of the six batteries might pull the overall voltage down. Guess not. Anyway, thanks...I'll not worry about it. Not a big deal at the marina anyway...just thinking ahead for an upcoming extended cruise.
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