I have a li-ion powered dremel that wasn't being charged properly by the standard charger. I added 2 bullet connectors to it and now I charge with my RC chargers. I just put some electrical tape over them since they are wired directly to the battery.

No issue charging a battery while it's in your radio.

You might be better off putting in a barrel connector since it's just a hole and it would be easy to make a charging lead.