Yes, if you are connected to shore power leave the switch in the "use" position. This will charge ALL batteries, usually. The only time to use the "store" position is when you want to remove all drainage from the coach battery. That's what it's for...like if you had to leave it somewhere, where there was no electricity available. Others will say theirs is wired differently...the gas detector etc...still works on theirs. It's all according to who did the wiring that day.
When you are plugged in, the converter powers everything 12V AND charges the batteries, but that switch must be in the use position or else the batteries are missing out on being charged. You won't realize it, cause everything seems to be working. It's easy for the kids or guests to accidentally press the store switch as they try to turn other things on or off. When it's in the store position, the coach battery is theoretically disconnected from everything.