The in-line headset battery provides an additional portable power source for Micro System Headsets. Micro System headsets have a rechargeable battery in the headset headband. the headset battery allows the headset to work as an autonomous intercom and provides power to portable radio interface equipment and other micro system accessories. The in-line battery is designed to connect between a micro system headset and any other item of Micro System equipment and can be used to provide the following functions. The in-line battery can be used as a back up battery when the internal headset battery is discharged The in-line battery can be used as an alternative power source when the internal battery is disabled. The in-line battery can be used to extend the life of older headsets as an alternative to replacing headset batteries NOTE. Whilst the in-line battery is connected to a Micro System Headset the internal headset battery is disabled. The in-line battery provides twice the power of the battery built in the Micro system headset. When two headsets are connected using a radio interface, one in-line battery will Power both headsets. When two headsets are connected using a headset coupling adapter, an in-line battery is required for both headsets. The In-line headset battery provides an additional/alternative portable power source for Micro System headsets.