4 Truths about your phone’s battery life: Overcharging, overheating, fast charging

By | May 27, 2020

1. Your phone battery isn’t changing anytime soon

All mobile phones — and most personal electronics and electric vehicles — use lithium-ion (li-ion) rechargeable batteries. It’s a tough slog to create batteries that last longer, because battery technology hasn’t changed in decades. Instead, much of the recent progress in battery life has come from power-saving features built into devices and from making the software that manages charging and discharging more efficiently, so you sip power rather than guzzle it. 

Unfortunately for mobile phones, the focus on extending battery life is generally on cars, satellites and your home’s power system, areas where industrial batteries need to function far beyond the two or three years we expect from our mobile devices.

Another force working against our phones is their battery size. Compared to an electric car battery, a phone’s power source is minute. For example, the Tesla 3’s rechargeable battery has a battery capacity over 4,000 times greater than the iPhone 11 Pro Max. 

2. Fast-charging won’t damage your battery

A conventional charger has an output of 5 to 10 watts. A faster charger can improve that by up to eight times. For example, the iPhone 11 Pro and Pro Max come with an 18-watt fast charger, the Galaxy Note 10 and Note 10 Plus have 25-watt chargers in their boxes. Samsung will sell you an extra-speedy 45-watt charger for $50.

Unless there’s some technical flaw with your battery or charger electronics, however, using a fast charger won’t do your phone’s battery any long-term damage.

Here’s why. Fast-charging batteries work in two phases. The first phase applies a blast of voltage to the empty or nearly empty battery. This gives you that blazing charge of from 50 to 70% in the first 10, 15 or 30 minutes. That’s because during the first phase of charging, batteries can absorb a charge quickly without major negative effects on their long-term health. 

For instance, Samsung promises its 45-watt charger can go from zero to a 70% charge in half an hour. Apple says the fast charger that comes with its iPhone 11 Pro can hit a 50% charge in 30 minutes.

You know how it seems to take as long to fill up that last 20 or 30% of the battery as it does to charge the first 70 or 80%? That last part is the second charging phase, where phone-makers have to slow down and carefully manage the charging speed or else the charge process actually could damage the battery.

Damage is rare if everything’s well-managed inside. A battery’s management system closely monitors the two charge phases and drops the charging speed during the second phase to give the battery time to absorb the charge and avoid issues, which is why it can take 10 minutes to get those last few percentage points. 

The case of the Samsung Galaxy Note 7’s tragically exploding battery resulted from battery design flaws rather than from the phone software’s battery management techniques.

3. You can’t overcharge your phone battery

Overcharging used to cause anxiety among phone owners. The fear was that keeping a phone constantly plugged in could charge a battery beyond its capacity, making the battery unstable, which could degrade overall battery life or build up too much internal heat and cause the battery to burst or catch fire. 

A battery’s management system is designed to shut off the electrical charge once a battery reaches 100%, before it can overcharge. 

Unless something goes wrong with the battery circuitry, you can’t overcharge a modern phone, they have protection built in to exactly stop that from happening. Remember that you can, however, put a battery under strain as you head to a 100% charge, as detailed above. (It’s why electronic-vehicle makers cut off the charge on new batteries around 80%.)

Apple takes a clever approach to this problem in the iPhone’s iOS 13 software that charges your iPhone battery to 100%  without doing long-term damage. 

If you frequently keep your iPhone plugged in during the day or while you sleep, you can turn on an iOS 13 battery setting called Optimized Battery Charging that will monitor your charging schedule and hold your iPhone’s battery charge at 80%, keeping it out of the stress zone. After that point, it’ll top off the charge to 100% right before you regularly unplug your phone. This works best for people who have a regular charging pattern.

For a manual approach, you can also unplug your phone when it hits an 80% charge, but the trade-off is you might miss out on additional hours of use that you’d get from a fully charged phone.

4. High temperatures can damage your battery

Heat is a true enemy to your battery. High temperatures are known to reduce a battery’s lifespan over time.  You’ll want to keep your phone out of strong sun, away from window sills and off the dashboard of your car to prevent overheating, which can make the battery less efficient over time. In extreme cases, an overheated battery could explode. Temperatures as high as 86 degrees Fahrenheit (30C) can decrease a battery’s effectiveness,