Originally Posted by vanamaniac
OK..that helps...so if the current isn't cut off until it reaches 40 amps (with the breaker I bought)..should I reconsider and buy a 25 or 30 watt breaker so it shuts off the current to the secondary battery even sooner? wouldn't a 25 amp breaker make it easer on the alternator cause it would not be charging the secondary battery as much if the 25 amp breaker shuts current flow down sooner(than a 40 amp)?
The breaker is there to protect the wiring, primarily, against shorts that would overheat it and possibly start a fire. The breakers should be sized to match the capacity of the wiring, so you need to know the wire size to chose the proper breaker. The breaker size will have no real affect on how things work unless it is so small it trips all the time, when trying to charge the batteries. Our Roadtrek has a #4 wire to the rear with an 80 amp breaker. Older ones used a #6 wire with a 50 amp breaker, IIRC. If you can get to a section of the wire, you should be able to clean it off and it will say the gauge size on it.
Don't worry about the amperage to your batteries, unless the alternator goes bad and puts out way too much voltage, they will take only what they can handle. Get the biggest breaker your wiring can handle.