Why do mobile batteries die so fast? and why can they only be recharged so many times before they won't hold a useful amount of charge anymore?
Many researchers try to find ways to make batteries that charge faster, last longer and can be recharged and discharged many more times than today's batteries that are on the market. However, it is impossible to make a truly everlasting battery. So far there is nothing that suggests we can break the fundamental laws of science to get that elusive battery.
Battery scientists and engineers call the main problem "capacity fade". People regularly wonder about it with questions like "Why won't my battery hold a charge?" and complaints like "I just recharged this thing, and it is already out again!".
It’s a result of what is called the second law of thermodynamics, which states that whenever some real process happens, it creates a certain amount of wasted energy along the way that can never be recovered. Any time a battery is charged or discharged, there’s a little bit of wasted energy which is basically a bit of wasted capacity in the battery that cannot be recovered.
To understand how this works, think about battery use like transferring water between two cups. Using a battery is like emptying the water from one cup into the other, and charging the battery involves pouring the water back into the first cup. Even if you do it one or two times without spilling a drop, there’s always just a little tiny bit left in each cup that you can’t pour out.
Just as water inevitably goes missing, when pouring from one cup to another, more energy is required to charge the battery than it actually stores and less energy comes out that is stored in it. The proportion of wasted energy to stored energy grows over time.
In fact, the more you use a battery, the more energy gets wasted, and the sooner the battery will reach a point where it’s dead and can’t usefully be recharged. But knowing why your battery keeps dying is only half of the problem. How can you use this information to protect your phone's battery life?
One important thing to do is avoid exposing your battery to extreme temperatures. Heat above 35 degrees Celsius noticeably accelerates the cathode's decline. Battery capacity is also diminished at low temperatures, but this is (usually) a temporary effect. For ideal performance, keep your battery at a temperature between 16-22 degrees Celsius. This may mean removing any phone cases during charging and even unplugging it during charging if it gets too hot.
Speaking of charging, here's another tip: don't charge your battery to 100%. It might seem counter-intuitive, but unless you need a full charge for portability's sake the battery will fare better on a partial one. High temperatures actually damage the battery by raising the voltage, and when you charge a battery to 100% the voltage is also raised to its limits.
Unfortunately, these techniques only prevent a battery from losing its efficiency. There's not much you can do to rejuvenate an ageing battery without specialist equipment – but at least you can now stop yours from getting any worse!