Although cell phone batteries are made to be charged and recharged, like any other battery they will need to be replaced after some time. Depending on how frequently you use your phone, and whether you use data-intensive applications, this time frame can be as much as two years, or as little as six months. There are several things that you need to look for to know when to replace a cell phone battery.
Battery Life Halved
It is normal for battery life to decrease at a steady rate over the life of the phone's battery, but when a phone's battery life only lasts half as long as it did when you first used it on a full charge, then you will probably need to think about replacing it. Unfortunately, once a battery gets to the point where it can only charge halfway, you will notice the remaining battery life deteriorate at a much faster rate than previously, and if you don't want your phone to die out, then you should replace it as soon as possible.
Charging Takes Longer
If charging your phone fully used to take only a few hours, but now takes a full night, this can be another sign that it is time to change your battery. Cell phone batteries operate using several cells, and after awhile a "Memory Effect" may occur. This effect is a condition where a battery will only use cells that have been discharged and charged on a regular basis, which will leave several cells unused. This means that the remaining cells will have to work harder, and your overall charge time will be increased.
A final way you can tell when a battery needs to be replaced is if the shape of the battery has changed. A battery in good standing will be flat on all sides. However, an overused battery tends to swell on the sides facing the battery door and the interior of the phone. When this occurs, it is especially important to get the battery replaced as soon as possible, as a swollen battery can erupt, permanently damaging your phone and possibly causing injury to the user.