Do Two Batteries Wired in Parallel Need to be Exact Same

Published 02/19/2019

Question:

I saw your diagram on how to wire two 12 VDC batteries together in parallel and keep 12 VDC. Three questions on that.... 1. Does it effect in any way a boat motor charging both batteries versus just the one it charged while running before adding the second battery? 2. Do both batteries have to be the EXACT same brand, model, amperage or anything else? 3. Can I come off the positive and negative of both batteries for running 12 VDC items like a fish finder, LED lights....and the like? Thanks.

asked by: Rich

Expert Reply:

Connecting two batteries with different capacities in parallel is technically fine since the batteries will be operating at the same voltage. Charge and discharge current will be shared, based on capacity. It is best if the batteries are of the same type and age. So your boat alternator charging one or two batteries would be the same and not a problem.

Lastly, yes you'd want to wire your accessories to the battery bank in the same "parallel" way.

expert reply by: Jameson C