If your cellular phone battery isn't charging, it could be caused by a number of things. In some cases, a battery could be old. In other cases, the jack where the charger plugs in to the phone could be defective. In other cases, the internal charging circuitry in the phone may have failed.
Try charging the battery using another phone that uses the same type of battery. If the battery charges and works normally after being charged in another phone, it is very likely that the problem isn't with the battery. The problem is likely with the charging circuitry or jack where the charger plugs in to the first phone. If the phone is under warranty, report the problem to your cellular provider. If the phone isn't under warranty, it might be worth talking with a cell phone repair service about the cost of replacing the jack or charging control circuitry.If the battery doesn't charge in the second phone, it may be a defective battery. Try a new battery and see if the problem is solved.
In some cases, a cell phone battery may fail after a year or two. A battery is only designed for a certain number of charge and discharge cycles. If the battery in your phone will not charge, try buying a new battery. If the new battery works, the problem was a worn-out battery. However, if the new battery still won't charge, the problem is likely the charging jack or charging circuitry in the room.
Testing a Cell Phone Battery
To test a cell phone battery, remove the battery and look at the label to establish what the battery voltage should be. Most are 3.4 to 4.5 VDC. Check the voltage by placing the red lead of a voltmeter on the positive (+) contact and the negative lead on the negative (-) contact. If the voltage is OK, you may want to check the amperage. To do this, you will need to know how many miliamps the battery is supposed to output. A web search should turn up this information. If you are seeing a rapid drop in amperage, this indicates a quick discharge of the battery and likely means that the battery is worn out.