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'.
A rechargeable battery, whether Ni-Cad or Ni-MH, can be recharged typically 500 times, give or take a bit.
If the battery is four years old and it has been caned, as your description indicates, it is likely well past its sell-by date and needs replacing - they don't cost the earth, assuming you can still get one!
You don't say whether you measure 4.02V after the battery has been flattened during use in a normal day or whether it is measured directly after recharging. It is highly unlikely that you would measure this voltage if it had been flattened.
The nominal voltage of a Ni-Cd or Ni-MH cell is 1.2V, but when new and fully charged and left to settle they will usually measure around
1.25V. Multiplying 3 x 1.25 gives 3.75V.
There is no such thing as "overuse between charges" for any type of battery. They simply expend their storage capacity during use. The length of use which can be expected is variable depending upon the rated capacity, whether the battery is new or old, and the proportion of time the handset is spent in receive mode as compared to transmit mode. The battery will be more heavily loaded during transmission than when receiving and the length of operating time while off the base station will be reduced. The best guide as to the length of time for "normal" handset operation will probably be in the user guide obtained with the cordless phone. The more time the handset battery is flattened, the more charging cycles it will be subjected to. The more charging cycles a battery is subjected to the greater is the reduction in the rated capacity, and eventually the battery will not hold a charge for any length of time to provide its normal length of operation.
Since the phone is only a few years old there will be no problem obtaining a new battery.
Four years of hard use & its time for a new battery! With a typical lifetime of 500-1000 cycles (under very good operating conditions) & figure maybe 250 discharges a year & you get a 2-4 year life.
If its got less talk time between recharges than it did when new, it _is_ probably defective...
Its only overused if it is used after the batteries are discharged :)
If the built-in battery management if working correctly, using the handset until it cuts off from low battery should not hurt in - BUT - it should be promptly recharged. Actually nicads like being used & generally give very good life. End-of-life is a gradual reduction in capacity (as neighbor may have noticed).
Usually "the designers" spend a few extra $ to let the consumer know these things & publish the document as an instruction manual, which the consumer thinks is extra packing only to throw away...
If it really took "several days" to recharge something is probably defective. 10-14 hours (overnight) is what I see most...
Get the information from the neighbors manual (hahaha) or look up the model # on the web & d/l it.
I have found most phone manuals available on the manufactures web site. Below is part of a pdf on a Sony 900MHz from ~1999. The handset battery referred to as BP-T23 is: 3.6V, 600mAH (3 std. AA cells).
Quote from pdf...
Battery duration A fully charged battery pack lasts for about: Approx. 7 hours when you use the handset continuously Approx. 6 days when the handset is in standby mode.
Notes: The battery pack will gradually discharge over a long period of time, even if not in use.
If you leave the battery pack in the handset without charging it, the battery pack will be completely discharged.
It may require several times of charging to recover its full capacity.
To obtain the best performance from the battery : Do not place the handset on the base unit after each call. The battery works best if the handset is returned to the base unit after two or three calls. However, do not leave the handset off the base unit for a long period of time as this will completely discharge the battery pack.
When to purchase a new battery pack:
If the battery lasts only a few minutes even after 10 hours of charging, the usable life of the battery has expired and needs replacement. Contact your local Sony authorized dealer or service center, and ask for a Sony BP-T23 rechargeable battery pack.
Note : Battery life may vary depending on usage condition and ambient temperature.
If you do not use the handset for a long period of time, remove the battery pack after charging for more than 10 hours. This maintains battery life.
Specifications - Handset Power source Rechargeable battery pack BP-T23 Battery charging time Approx. 10 hours Battery life Standby: Approx. 6 days Talk: Approx. 7 hours
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