My neighbour has a four year old 3.6 volt 850 milliamp/hr cordless telephone
handset battery which is used frequently and often for long periods; i.e.
talking continuously for several hours. Removed from the handset and with no
load the open circuit voltage of the three cell battery is 4.02 volts.

She feels battery is defective; I feel it is overused between charges!

Can anyone suggest please;
a) How long, continuously, can such a battery, when fully charged,
typically, operate the handset before requiring to be placed back onto the
main unit to be replenished?
b) What would be a typical or designed 'duty cycle' for a cordless phone.
i.e. what percentage of use away from the main unit versus placed on the
main unit for recharging?

It would seem that the designers must base the battery capacity of some sort
of average expectation of the amount of handset use away from the main unit.

Similarly; we recently mislaid our 900 mhz cordless handset, for nearly a
week. When found its battery was 'flat'. It took several days for the
battery to recharge to operate 'normally'.

Comments welcomed. TIA