"Bob" wrote in message
...
I have a 22' Chaparral with a Merc 350 300HP. I do a lot of lake
boating, long days, and would like to have a reserve battery to start
the boat in case the primary drains while docked or just for
emergency.

I'd like to wire in a combiner and switch as show here
http://www.skingcompany.com/manuals/C50.pdf

I am not sure what amp rating I need for the combiner and switch. Can
someone help with this. I don't care about saving pennies, want the
best system for safety.

Thanks,
Bob

Get a Guest Dual battery switch, West Marine or any other marine supplier.
A 50 amp combiner as you do not have a 100 amp alternator likely on a 350
cid engine. The 50 amp combiner is $80 at West, hook the two batteries
together with the combiner, I did it at the Guest switch. Instructions in
the combiner. I run my electronics off the second battery and added a
single battery switch in the feed to the fuse panel, so I can shut off all
the power in the boat. You can add a small switch in the combiner to shut
it off, if you want to charge only one battery. I did not.