If you charge your radio at the field with a peak charger then you must remove the battery. The diode in the transmitter will not allow the field charger to sense the peak.
And some modellers are now using LiFe/L-ion batteries in thier transmitters. Again, these should be removed to allow the charger to sense the peak and in case of fire.
If you are using NiCd batteries or NiMh batteries and a timed slow charger you can safely leave them in the radio.
