Typically the batteries in a cordless phone will last for 1 to 3 years. As long as the batteries, which are typically made of nickel cadmium (NiCad) or nickel metal hydride (NiMH), are allowed to discharge fully before recharging they will last their full lifespan. But if your cordless phone battery still isn't holding a charge when off the base, it may be time to change the batteries. When you hear that annoying beep while you're talking to your friends it's time to open up the phone and take a look!
Allow the old battery to discharge completely. It's a good idea to do this on a regular basis, as "cooking" (overcharging) the battery can significantly shorten its lifespan and make it less likely to hold a charge.
Locate the battery cover on your cordless phone and remove it. Take the battery out of the phone carefully so that the connecting wires don't snap.
Unplug the battery connector from the inside of the telephone.
Identify the model number of the battery. It should be written on the battery itself, but if you have previously replaced it with a generic battery make note of the phone brand and model instead.
Bring the battery and information about your phone to the store. Many stores carry generic brand telephone batteries that list model compatibilities on the back of the package. Having the battery with you will simplify the process of locating the correct replacement.
Change the battery by connecting the new battery to the phone, making sure that the battery connector fits back in smoothly. If it doesn't you may be putting the connector in upside down.
Replace the battery cover and put the cordless back on the charger base. Allow time for the new batteries to charge completely as they will not be charged when they first come out of the package.
Let the old batteries cool down for at least 30 minutes prior to disposing of them.
Check with your local recycling program to see if they recycle NiCad or NiMH batteries. You can also check the Rechargeable Battery Recycling Corporation's website to find somewhere in your area that recycles cell and cordless phone batteries (see Resources below).
Never incinerate or dismantle rechargeable battery packs.