Bumpyroad and Dakota 98 ~
Here is what I used. Mounted to the under wing with 8 gauge wires running into the interior battery. Then just clip your battery charger leads to these terminals.
External Battery Jumper Block from Summit Racing. You'll have to search it at Summit. I can not remember how to do a link!!!
External Battery Jumper Block, Charging Post, Kit Then adding a 2nd battery is a piece of cake. Set it in the bed below the terminals and run 8 gauge wire up to it. I used an Anderson connector for quick easy on/off connection.