Why Your iPhone Battery Keeps Dying Before 0% (And How to Fix It)

iPhone battery draining
Jennifer Bui/Thrillist
Jennifer Bui/Thrillist

If you own an iPhone, perhaps you've experienced the mystifying wonkiness of your battery icon. Your battery goes below 20% and total anarchy ensues: the power level jumps around, and your phone shuts off long before you've reached 0%. You've probably also noticed that sometimes it takes a weirdly long time to dip below 100% after a full charge.

So what's the deal? Is this some grand conspiracy by Apple to alter your perception of time? Is this just the result of Apple releasing a glitchy new iOS update? Is your 6S faulty? Are you charging your phone wrong? Turns out it's a bit more complex than that, but here's the deal, and how to fix it.

man charging dead iphone in car
<a href="http://www.shutterstock.com/gallery-606352p1.html?cr=00&amp;pl=edit-00">think4photop</a> / <a href="http://www.shutterstock.com/editorial?cr=00&amp;pl=edit-00">Shutterstock.com</a>

Your iPhone lies about how full the battery really is

Lithium ion batteries are all kinds of quirky, and it’s actually bad for them to be at 100% or fully depleted to 0% because it messes with their longevity. So iPhones, and other smartphones that use Li-ion batteries, purposely throttle how much power they demand from the battery.

When it's plugged in, your iPhone will cease charging before the battery actually reaches a full 100%. It will also preemptively shut down before it’s completely out of juice. The latter not only protects the battery, but also ensures there’s enough power in there to complete a safe shutdown, and to issue the dreaded “needs charging” screen when you try to reboot.

All that's well and good. The thing is, this sort of compensating at either end of the battery cycle confuses your phone over time, and that's the reason why it will sometimes shut down when you don't expect it, way before your indicator reaches zero. 

iphone 6 restarting
<a href="http://www.shutterstock.com/gallery-2280761p1.html?cr=00&amp;pl=edit-00">Attila Fodemesi</a> / <a href="http://www.shutterstock.com/editorial?cr=00&amp;pl=edit-00">Shutterstock.com</a>

And it only gets worse in extreme temperatures

As we’ve discussed before, extreme temperatures can have quite an adverse effect on your iPhone battery’s performance, and you’ll notice that jumpiness from low battery to shut-off is probably even more pronounced on a hot day at the beach or a blustery walk to work during the winter.

But you can fix it!

It would be nice if Apple found its own fix for this idiosyncrasy, but in the meantime, there is a manual workaround to get your battery indicator back to normal. Essentially, you need to recalibrate the battery, which requires very little other than patience.

To begin the process, you’ll need to drain the battery entirely so that it shuts itself off -- go make a crazy-good Snapchat Story or stream a few HD videos and you’ll get there in no time. Then, plug your phone in and let it charge all the way up to 100% without using it. Keep it plugged in an extra hour or two, just to ensure it’s fully charged (patience, people). Next, you’ll perform a “warm restart,” holding down the home and lock buttons simultaneously for a few seconds until the Apple logo appears on the screen. Cool, now do the whole thing over again. More Snapchat! After you repeat the whole process a second time, you should be back in business with an accurate battery indicator once again. Hallelujah.

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Joe McGauley is a senior writer for Thrillist. His palms sweats whenever his phone drops below 20%.