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How Lithium Ion Batteries Work


Many of the questions we get here at Phone Medics Plus relate to phone batteries. Why does my battery stop working? How can I improve my battery life? Why isn’t my battery charging/holding charge? With that in mind, we’ve put together a quick primer on just how your the battery in your phone, tablet, or PC works.



How Batteries Work

Every battery - from the button battery in your watch to the AAs in your remote control to the battery in your car to the battery in your phone - has three basic components: a negative electrode (the anode), a positive electrode (the cathode), and an electrolyte. In a fully charged battery, the anode is holding onto a bunch of electrons. When the battery begins to discharge, those electrons start to move from the anode to the cathode, through the electrolyte. That movement generates the electricity your device uses. The more electrons make their way to the cathode, the less power the battery puts out. Once the battery isn’t putting out enough power for your device to use, we call the battery dead.

Now, in a non-rechargeable battery - like those AAs in your remote - once most of the electrons have made the trip from the anode to the cathode and the battery is dead, then it’s time to throw the battery out and replace it. Rechargeable batteries like the ones in your phone or laptop are a little different. With those batteries, you can apply electricity to the battery (by plugging your phone in), and the flow of electrons gets reversed. So now the electrons are moving from the cathode back to the anode. Once they’re back, then the battery is charged again.

A lithium ion battery like the one in your phone has a few more components in addition to the basic three. Most lithium ion batteries have a separator to keep the electrodes apart, as well as sensors and other electronic components that allow the battery to interface with your device. In a lithium ion battery the electrolyte is a chemical solution containing lithium ions. When the battery is discharging, the lithium ions move from the anode to the cathode through the electrolyte solution, generating electrons and creating electricity. When the battery is charging, the lithium ions move back to the anode.

Why Batteries Wear Out

So the next question you may be asking is, if the battery works by moving lithium ions back and forth, then why does your battery eventually wear out? Why doesn’t the battery in your two-year-old iPhone last as long as it did when it was new? Well, as it turns out, there are a couple of reasons. First of all, the chemicals in the battery start breaking down almost as soon as the battery rolls off the assembly line. In other words, your battery basically has an expiration date, and will eventually stop working even if it were never to be used at all. Second of all, the process of charging and discharging a battery increases the wear and tear on the battery’s components. In other words, your battery has a limited number of charge cycles - the number of times you can discharge and recharge the battery - before it starts to wear out.

As your battery starts to wear out, you may notice that even though you plug your phone in until the battery meter reads 100%, it doesn’t last as long. At first, that might seem weird: clearly the battery isn’t operating at 100% of the capacity it had when you bought it, so why does it still say 100%? The reason is that your phone’s battery meter tells you the current capacity of the battery, not the original capacity. So when your older phone says it’s 100% charged, it means it’s at 100% of what the battery will hold now. Even though it doesn’t hold as much as it used to, it’s still full.

Think of your battery as a bucket. Every time you charge it, you’re filling the bucket with water, and every time you discharge it, you’re pouring the water out. But every time you do that, the water leaves behind a small layer of sediment that sticks to the bucket. The first time you fill the bucket and dump it out, the sediment layer isn’t enough to make a noticeable difference in how much water the bucket holds. Eventually, though, the sediment builds up and the bucket doesn’t hold as much as it used to. Now it takes less water to fill it all the way up, and less time to pour all the water out. The bucket can be 100% full, but still have less water in it than it did the first time you filled it up. Your battery is the same way. After a couple years it can be fully charged, but because its capacity is reduced, it charges more quickly, and takes less time to run down.

When that happens, it’s time to start thinking about replacing your battery. A new battery can make your old phone feel like new again. Here at Phone Medics Plus, battery replacement is one of many services we offer. When you bring your phone to our repair facility at 91 E. Merritt Island Causeway in Merritt Island, our skilled repair techs can replace your battery and give your phone a new lease on life. Give us a call or book your appointment online today!

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