Panasonic CF-20 Series Operating Instructions And Reference Manual page 141

If the battery pack got lodged in the slots, push the middle of the battery pack.
n
The battery indicator lights when the battery pack is properly inserted with the AC adaptor connected.
Four battery packs can be inserted simultaneously. Each of them can be inserted in any slot.
When removing the battery pack, pull it out in the opposite direction of attaching the battery pack.
Charging begins automatically.
The battery pack or battery charger will become somewhat warm during normal use. This is not a malfunction.