Most switches only leave the ground connected when in the off position... some don't even do that. I always charge my Fromeco LiIons (SuperReliaReg) while they are connected to the reg which is plugged into the RX. I also charge my ignition batteries while they are connected to the switch (installed in the plane) which is connected to the ignition. Never had a problem. I usually top off my NiCd or NiMh ignition battery in between flgihts (every two) so I never have to wait very long for anything to charge!!!

FWIW... the ignition instructions for my ZDZ-80 TELL you to watch for the spark on the plug when setting up the ignition timing. Seems to be OK to me!