BTS Master MT8221B and MT8222B : General Information : Battery Replacement
  
Battery Replacement
The battery can be replaced without the use of tools. The battery compartment is located on the lower left side of the instrument (when you are facing the measurement display). Slide the battery door down, towards the bottom of the instrument, to remove it. Remove the battery pack from the instrument by pulling straight out on the battery lanyard. Replacement is the opposite of removal.
Battery Compartment Door
Note 
Use only Anritsu approved batteries, adapters, and chargers with this instrument.
The battery that is supplied with the BTS Master may need charging before use. The battery can be charged while it is installed in the BTS Master by using either the AC‑DC Adapter or the 12‑Volt DC adapter, or separately in the optional Dual Battery Charger. Refer to your Technical Data Sheet for Anritsu part numbers. Refer to section Symbols and Indicators for a description of battery symbols.
Caution
When using the Automotive Cigarette Lighter 12 VDC Adapter, always verify that the supply is rated for a minimum of 60 Watts @ 12 VDC, and that the socket is clear of any dirt or debris. If the adapter plug becomes hot to the touch during operation, then discontinue use immediately.
Note
Anritsu Company recommends removing the battery for long‑term storage of the instrument.