Battery Combiner 200
The Combiner 200 is a voltage-sensing relay (13.1 volts) which connects two batteries together when either is receiving a charge. When the charging ceases, the relay opens so that each battery operates independently. Supplemental battery banks can be added by using an additional combiner for each bank. You never have to worry about switching to "BOTH" when your engine is running and forgetting to switch back to save your starting battery from discharge when you stop.
For alternators greater than 200 amps use the Combiner 600