By: Grid Michal
When I run down the house battery and want to start the engine, I switch to the starting battery. After starting the engine, can I switch from the starting battery to both batteries or the house battery? Or should I start the engine, warm it up, then stop the engine, use the battery switch to switch to both batteries and then restart before the house battery can pull down the starting battery?
Unless the battery selector switch has a diode specifically protecting the charging system when the selection is made while the engine’s running, my answer is to (as you said) start the engine on the cranking battery, make sure the engine’s OK, shut the engine off, switch to BOTH and restart the engine. Remember that a deep-cycle and a standard cranking battery have different charging rates, so the house battery may not get the full anticipated charge. If you have two types of batteries, then you may want to just start it on the house battery. However, installing a battery isolator will resolve all the problems.