Casella CEL CEL-393 - Manual (Page 88)

estimated to be in the order of 4 hours total when used continuously in
filter mode.
Rechargeable NiCad cells may also be used, and these are available in
pairs complete with a suitable charger unit under the part number
CEL-4185. It should be noted that they provide a shorter duty cycle.
At switch on, the instrument defaults to the battery check mode for
approximately 25 seconds, during which time it displays the on load
battery voltage. End of battery life is 6.5V for the A version and 6.8V for
the B version. It is determined by a change of 0.5dB under reference
conditions.
To check the battery during a measurement sequence, use the key
sequence 9F. When the instrument is in this mode the instrument does
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