Applicable Model: 2640
The 2640 field strength meter can be battery operated or with external AC adapter. It accepts regular AA size alkaline batteries (1.5 V) or NiMH rechargeable batteries (1.2 V) rated for 2700 mAH.
When using external AC adapter, if NiMH rechargeable batteries are inserted in the battery compartment, it will charge the batteries when the unit is in power off state. If alkaline batteries are inserted in the battery compartment, DO NOT connect the external AC adapter input. The unit cannot charge batteries that are not rechargeable. Doing so may cause potential hazards such as battery leakage or explosion.
Note: External AC adapter can be used even if no rechargeable batteries are inside the battery compartment.