S820E Microwave Site Master™ User Guide : General Information : Instrument Description : Battery Information
 
Battery Information
The battery that is supplied with the Site Master may need charging before use. It can be charged using either the AC‑DC Adapter or the DC adapter. Refer to Status Tool Bar for a description of battery symbols. The batteries are typically charged in the instrument.
Note 
Use only Anritsu Company approved batteries, adapters, and chargers with this instrument.
The batteries will charge at a faster rate when the instrument is turned off or is set to standby mode. Charging the batteries while the instrument is running requires a longer time to reach a full charge.
To prolong the useful battery life, the internal charging circuit monitors battery temperature. Normal charging occurs when the battery temperature is between 0 °C and 45 °C. Charging is paused if the internal battery temperature is beyond this range.
Caution 
When using the Automotive power outlet adapter, always verify that the supply is rated for a minimum of 60 Watts at 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.
Refer to Battery Replacement for additional information on replacing the batteries.
Note 
Anritsu Company recommends removing the battery for long‑term storage of the instrument.