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Author Topic:   Charging Two Batteries In Parallel
MAGOO posted 06-05-2007 04:05 PM ET (US)   Profile for MAGOO   Send Email to MAGOO  
Can my one outboard motor charge two batteries in parallel?
Bella con23 posted 06-05-2007 04:50 PM ET (US)     Profile for Bella con23  Send Email to Bella con23     
What size outboard? Are both batteries exactly the same?
Personally, I have made a habit of charging #1 battery on the way to my destination then switch over to #2 battery on the way back.

This method eliminates the guesswork of whether or not the batteries are balanced on the charging system.

jimh posted 06-05-2007 07:20 PM ET (US)     Profile for jimh  Send Email to jimh     
A charger cannot tell when it is connected to two batteries in parallel. It just delivers charging current and tries to raise the voltage of the load it is attached to.

You can charge two batteries in parallel, but it is not particularly recommended.

dburton posted 06-05-2007 11:59 PM ET (US)     Profile for dburton  Send Email to dburton     
While this is might be killing a fly with a sledge hammer, this would solve your problem:

The problem with charging batteries that are in parallel is that they are in parallel. That is, if one of the batteries doesn't hold a charge then the weaker battery will draw down the stronger battery until they are equal. Eventually you will not have enough power to do what you need in either battery. If you have a battery switch that has a "both" setting then they will be in parallel. They will charge together but they will also discharge together and also balance each other. If you can always remember to switch after charging to "one",or "two" or "off" then it can be OK. But, not many, including me will remember to do that 100% of the time. The sound of the starter motor spinning but without enough juice to raise the gear up the worm gear is enough to make a grown man cry.

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