Why Is Your Phone Battery Constantly Dying?
Why do batteries die? Also, why do they stop holding a useful amount of charge after multiple recharges?
My little boy asked me such a question years ago when his battery powered toy car stopped moving and was curious about something he called the “never-ending battery”.
Also, this question has probably occurred to all mobile phone users trying to send one last message before the screen turns off.
Research like mine, which continues around the world, aims to produce batteries that charge faster, last longer, and can be recharged and discharged many times more than today.
But as much as we want it, it’s impossible to make a truly infinite battery. I have taught thermodynamics for over 30 years. So far, nothing has implied that we could break the fundamental laws of science to get that elusive battery.
Battery scientists and engineers call the fundamental problem “capacity reduction.”
Ordinary people ask, “Why isn’t my battery holding a charge?” They wonder about this situation with questions like “I just charged this thing and it’s gone again”.
This is a consequence of the second law of thermodynamics and means that whenever real progress is made, a certain amount of energy is wasted in the process, which can never be recovered.
Whenever a battery is charged or discharged, there is a small amount of wasted energy; that is, there is a small amount of capacity in the battery that is wasted and cannot be recovered.
To visualize how this situation came about; Think of battery usage like transferring water between two glasses. Using a battery is like pouring water from one glass to another. Charging the battery requires pouring the water back into the first glass.
Even if you do this once or twice without spilling a drop on the floor, there will always be a small amount of water in both glasses that you cannot pour.
Now imagine filling and emptying water hundreds or even thousands of times over a period of two or three years (for a mobile phone) or 10 to 20 years (for an electric car).
Over time, thousands of small and large things that go wrong add up, causing a sizable amount of water to be lost.
Even the spilling of a barely visible drop (say, a tenth of a millimeter) would add up to a full liter if it happened 10,000 times. This does not even include the fact that one of the glasses somehow falls over and loses much more water; for example, a leak may occur or the glass may heat up and cause evaporation.
Just as water is inevitably lost as it is poured from one glass to another, charging the battery requires more energy than the battery actually stores, and less energy comes out of the battery than the energy contained in it. The ratio of wasted energy to stored energy increases with time.
In fact, the more you use a battery, the more energy is wasted and soon the battery reaches a point where it is dead or cannot be usefully recharged.
Me and others are looking for ways to make these charge/discharge cycles smoother to reduce waste, but the second law of thermodynamics will always assure that there is no way to get rid of it completely.