blue seas add a battery

[ted burdacki]

hi , i have a yamaha 2005 115 hp f115txrd 4stroke outboard . the spec for the alternator is 25 amps. i would like to install a blue seas add a battery kit ,which would combine two group 24 ,batteries at times. is there any potential harm with this system to the alternator ,or batteries.i believe the voltage of 1 battery must be up to nominal 12volt,before it allows charging of the 2nd battery.

[rodbolt17]

nope.
ditch battery wing nuts for hex nuts and spray all connectors with a corrosion inhibitor and go play.
some call them battery combiners others say voltage sensitive relay.
all do about the same thing.
some are solid state some are not.