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post #1 of Old 07-24-2011 Thread Starter
maccauley123's Avatar
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Change Battery Selector While Engine Running?

I have searched the forums here and looked at Nigel Calder's book and can't find an answer I am comfortable with.

I have a 2 battery system, one for starting and one for house. They are both wired to a single 4 position battery selector switch. Alternator is wired to switch as is distribution panel.

I just had to replace my starting battery because apparently it was not getting charged all the way. My practice was to usually use the "Both" selector on the switch when running the battery so in theory both batteries would be charged. Apparently this was not working well, alternator might not be big enough, and only one battery was being charged fully. The house battery was charged and was 100% healthy and the starting battery had 0 health.

Recommended I start the engine usually with the starting battery and run the engine so it would stay topped up. Every once in a while while engine is running switch to the house battery to keep it topped up. For the most part there is very little draw on the house battery since it is just used for radio, GPS, etc.

Is it OK to switch between 1, 2 and Both while the engine is running? West Marine said it should be OK and Nigel says "the switch needs to be of the make-before-it-breaks variety - both batteries are first brought on line (Both position) and then one disconnected". I take this to mean I can use Both to start and then switch to 1 or 2 depending on which battery I want to charge fully. Thoughts.

You will regret the things you did not do, more than the things you did.

Get out there!

Saco Bay, Maine
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