I know the phantom 2 manual suggests connecting batteries in the on setting to top off when they are charged above a certain percentage.
Im not convinved this is a good practice with the p3- at least i am not comfortable doing it.
There is nothing special about the p3 charger, it is a regulated DC power supply. The charging smarts are all inside the battery including monitiring, balancing and switching between constant current and constant voltage at the appropriate time to ensure a long helathy life.
When we turn a battery on, some internal device, probably a MOSFET transistor, connects the terminals to the cells. Im wondering if to then conneft to the charger in the on position exposes the cells directly to the applied voltage of thecharger (ie bypassing the charging circuitry, at least momentarily). This would be bad. LIPO chemistry is very intolerant to over voltage during charge. Worst case scenario is cell rupture and fire with best case outcome being greatly reduced usable life.
Purely thinking out aloud here. I will at some stage dissasemble a pack and do some measurements.