I am installing AGM house battery with a very minimal electrical demand, only coupla LED lights, microwave, tea kettle, Maxxair Fan, and am just keeping it simple with using an on/off switch to parallel with my van battery only when I need to for recharging. Not going to be camping overnight in the van, just travelin'. Was wonderin' does it matter when I turn the switch on and join the batteries, like does the engine need to be off and alternator not spinning before I switch it on or can I switch it on or off when going down the highway if I had a mind to? Would a sudden load on the alternator mess up anything? Just not sure how all this works. Thanks.