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If you've ever noticed that your phone's battery goes from 60% to 50% in a matter of minutes, only to remain on 50% for what seems like ages, it probably means the battery needs to be calibrated.
Why Your Phone's Battery Percentage Becomes Inaccurate
This is a problem that occurs in most battery-powered electronics these days, so this process should work on iPhone, Android, and even tablets or laptops (almost all of which use lithium ion batteries). While it's really not that big of a problem, it can be a bit annoying when your phone says you have 25% battery left, only to look again and see that it's nearly dying.
The reason for this is simple. Batteries naturally degrade over time, and their capacity slowly decreases. But your phone isn't always great at measuring that---if your battery has degraded to 95% of its original capacity, your phone might still report that as 95% full, instead of 100% full (the "new normal"). Calibrating your battery can fix this.
How to Calibrate Your Phone's Battery
Luckily, calibrating your smartphone's battery is an easy task---it just takes a bit of time and patience.
First, let your phone drain completely to the point where it shuts itself off. You can confirm that the battery is completely dead by trying to turn it on---you'll usually be greeted with a dead battery icon before the phone shuts off again after a few seconds.
Next, without turning it back on, plug your phone into the charger and let it charge up to 100%, leaving the phone off the entire time it's charging. Some people suggest leaving it on the charger for an extra hour or so, just to make sure the battery gets all the juice it can, but that's completely up to you and not extremely necessary.
After that, turn your phone on and wait for it to boot up. Once it gets to the home screen, confirm that the battery meter shows 100%, then unplug it from the charger.
Once unplugged, the battery is now calibrated and you can begin to use your phone again like normal.
How Often Should You Calibrate Your Battery?
There's really no official rule on how often you should calibrate your phone's battery. And technically, you don't really need to do it at all if you don't care how accurate the percentage is, especially if you're vigilant about keeping the battery charged up anyway.
If you want the most accurate battery stats, you'll probably want to calibrate the battery every two to three months. Again, you can go longer if you want (I only do it every six months or so), just know that your battery percentage may be a little off.
Battery Calibration Doesn't Make the Battery Last Longer
You may see other articles discussing how calibrating your battery can prolong its lifespan, or improve battery life. But long story short: it doesn't.
In fact, the best way to keep your battery healthy is to perform shallow discharges, not run it down to zero regularly---which is why you should probably only calibrate it every few months or so.
However, according to Battery University, there's no apparent harm to calibrating your phone's battery, and it's recommended that you do so from time to time.