[Chuck v]

Ron,

You did not tell us which coach model you have, but most have separate systems for "house" power (interior lights, etc) and chassis power to crank the engine, etc. If you have a gas engine, the single battery is likely that one. The two in parallel are likely the house batteries. The three should not be connected together permanently (some coaches have a switch on the dash that closes a relay to do this interconnect momentarily to start the coach if the chassis battery is low...)

On my diesel coach I have eight batteries -- two in parallel for the diesel engine cranking - these are the chassis batteries; two in parallel for the interior lighting loads -- these are the house batteries; and 4 each 6 volt batteries in series-parallel making a high capacity 12 volt stack to power the inverter that can make 120 volts AC in the absence of shore power or generator power. These also provide the cranking power for the diesel generator that is on board.

If you disclose the model and year of the coach you have, members here may be able to give more specific answers to your question. Was there a specific behavior or symptom you are chasing that prompted you to ask this question?

Chuck