Bird Technologies 4421 - Manual (Page 19)

Installation
7
Batteries
The Bird 4421 RF Power Meter is completely portable and is powered from
internal rechargable nickel metal hydride batteries.
The batteries are shipped in a low charge state. It is, therefore, recommended
that you chrage the instrument for approximately 28 hours before using it for
continous operation.
 Note: Battery charging at temperatures greater than 45° C (113°
F) can result in reduced operational time.
CAUTION
Long-term storage of this instrument can affect battery performance and
reduce battery life. Do not store the instrument for long periods of time
without recharging the batteries (refer to page 40). Failure to comply may
result in reduced battery charge and shortened battery life.