Panasonic KX-TG8411HGB Service Manual page 17

Note for service:
The battery strength may not be indicated correctly if the
battery is disconnected and connected again, even after it is
fully charged. In that case, by recharging the battery as
mentioned above, you will get a correct indication of the
battery strength.
6.2.3. Battery Level
6.2.4. Panasonic Ni-MH Battery
Performance (supplied batteries)
17
KX-TG8411HGB/KX-TGA840FXB