Inserting and removing the batteries/rechargeable batteries
You can operate the bodypack transmitter either with batteries (AA, 1.5 V) or with the rechargeable Sennheiser BA 2015 battery.
Press the two catches and open the battery compartment cover.Insert the batteries or the rechargeable battery as shown below. Please observe correct polarity when inserting the batteries.► 
Close the battery compartment. The cover locks into place with an audible click.
Battery status
Charge status of the batteries:
► 
Charge status is critical (LOW BATT):
► 