Cause:

4 Cell NiMH pack freshly charged to absolute maximum causing automatic battery pack recognition to incorrectly identify it as a 5 cell pack.

Fix:

Allow 4 cell battery pack recovery time from charging during which it's voltage will reduce to below 5.6 volts.

Comment:

At switch on the receiver identifies the battery pack cell count on the criteria:

>4.5 volts recognised as 4 cells, alarm sounds when voltage drops to this level or below.

>5.6 volts recognised as 5 cells, alarm sounds when voltage drops to this level or below.

Immediatly after and for a short time after charging a 4 Cell NiMH battery pack can exceed 5.6 volts and therefore would be recognised as a 5 cell pack. The voltage of a 4 cell pack will drop below 5.6 volts very quickly in use, triggering the low battery alarm for a 5 cell pack.

This behaviour has been seen with the Hitec Optima telemetry receivers and may be present in other brands too.