Dual battery question

[burtonrider11]

Not sure if this should be in the engine section, if so, please feel free to move it. Anyway, I have a boat with Merc 5.7/Alpha. When I bought it from the PO, it had two batteries and a battery switch - I believe to be a standard Perko, it has the OFF, 1, BOTH, 2. When I got the boat, I noticed that each battery has it's own set of grounds/ground wires. When I did some research, it appears many people tie all their grounds to one battery, then connect the batteries to each other, via the negative terminal posts.

Is there any benefit to this? Would doing this charge both batteries even when running on 1 or 2? I have checked the batteries when running with a multimeter, and the non selected battery does not receive a charge. We typically start and run on one of the batteries and when moored, switch to the alternate battery to run the stereo and inflatables pump etc. Typically, I'll start and run with this battery on the return trip....

Just wondering if there is any benefit to tying the two batteries together via the negative terminals or if it's fine as currently. If not, I'll just continue on as we have been. Any insight would be appreciated!

 

[alldodge]

It's best to run all negative cables to the engine block where they are tied together.

To charge your batteries use an automatic charge relay (ACR) , this way when the motor is running it will charge both batteries. When the motor stops the batteries are separated. Will not effect your battery switch