Why this topic is so muddled in the first place

Anyone who owned a cell phone in the 1990s or early 2000s internalized a particular rule: drain it all the way down, then charge it all the way up. Otherwise the battery would “remember” a smaller capacity — the famous memory effect. Back then, that was actually correct. Those devices used nickel-cadmium or nickel-metal-hydride batteries, and the rule applied to them.

The thing is: those batteries haven’t been in our devices for about 20 years. Smartphones, tablets, laptops, headphones, smartwatches — they all use lithium-ion batteries today. And those work in a completely different way. What was right for NiCd batteries is often exactly wrong for lithium-ion batteries.

The real problem isn’t that people give bad advice. The problem is that the technology has changed, but the tips get passed down from generation to generation — like a family recipe nobody questions anymore.

How a lithium-ion battery ages — no chemistry class required

You don’t need to be a chemist to understand what wears out a smartphone battery. Three things matter:

Charge cycles. Every full charge from 0 to 100% counts as one charge cycle. A modern smartphone battery survives roughly 500 to 1,000 of these cycles before its capacity drops noticeably. It’s the total amount that counts: charging twice from 50 to 100% uses up one cycle, not two.

Heat. This is by far the battery’s worst enemy. Above 95°F (35°C) it gets uncomfortable; above 105°F (40°C) it gets seriously damaging. That’s exactly why leaving your phone on the dashboard in direct sun or in a parked car in summer is such a bad idea.

Voltage extremes. A lithium-ion battery is happiest in the middle. Completely empty (actually 0%) and completely full (100%) are both stress states. Constantly forcing the battery into these extremes makes it age faster.

That’s really all you need to know. Everything that follows — which tips actually help and which are just myths — flows from these three points.

The most common myths, fact-checked

“Drain the battery completely before charging.” Wrong — and actively harmful. As just explained, voltage extremes are stressful for the battery. Regularly running down to zero and then charging back to full accelerates aging. That’s the exact opposite of what you should do. The myth comes from the NiCd era and has stubbornly survived in people’s heads, even though it’s been outdated for two decades.

“Charging overnight is dangerous.” The real myth here is the idea that your phone would destroy itself or even catch fire if it stays plugged in after hitting 100%. It won’t. Both iPhones and Android devices regulate charging intelligently: once 100% is reached, the charging circuit reliably shuts off and only draws as much power as needed to maintain the charge. Overcharging doesn’t happen. What is true: the device then holds the voltage at 100% for hours, which marginally speeds up battery aging. If you want maximum lifespan, don’t charge to full overnight. If you don’t care that much, go ahead — it’s not dangerous.

“Only use the original charger.” A stubborn myth, sometimes fueled by manufacturers themselves. The truth: modern smartphones charge via the USB-PD (Power Delivery) standard, and it’s standardized. A certified charger and a decent cable are perfectly fine, regardless of brand. What you should avoid is dirt-cheap no-name power bricks from a discount bin without any certification — those can actually produce unstable voltages. But any reputable brand-name charger from any manufacturer is fine.

“Fast charging kills the battery.” Overstated, but not pulled entirely out of thin air. Fast charging generates more heat than slow charging, and heat is genuinely the battery’s biggest enemy. What matters is the degree: with moderate fast charging up to about 30 watts, the effect is small because manufacturers intelligently throttle the charging current once the battery temperature gets critical. With extreme fast charging beyond 100 watts, noticeably more heat builds up — that speeds up battery aging somewhat, but it’s not a disaster. If you use your phone normally and fast-charge occasionally, you’ll barely be able to measure the effect after two years.

“Putting your phone in the fridge protects the battery.” Please don’t. You actually hear this one occasionally — the idea is that cold must be good because heat is bad. Sounds logical, but it’s nonsense. The fridge produces condensation that can seep into the device and cause corrosion. The battery doesn’t like extreme cold either. Your phone doesn’t belong in the freezer — neither to “protect” it nor to “cool it down” after a hot day. If your phone is overheating, just turn it off and let it cool down in the shade.

“Battery saver apps extend your runtime.” Most of these apps are useless at best and counterproductive at worst. What they typically do is “kill” background apps — but modern operating systems already manage that themselves, and more efficiently. An app constantly running in the background to monitor the battery uses battery itself. Many of these apps also display ads, which costs even more power. The built-in battery features of iOS and Android are far superior to most of these apps — free and without tracking.

What actually helps

Enough about myths. Here are the measures that, according to current understanding, actually make a difference:

The 20–80% rule — for the cautious. Keeping your battery between 20 and 80% as much as possible is the gentlest treatment. Honestly: the real effect is measurable but small. Over two years, that might mean 10 to 15% more remaining capacity compared to careless charging. For many people, the effort outweighs the benefit — constantly watching the charge level gets annoying. If you still want to try: don’t regularly run down to zero, and don’t leave it plugged in at 100% for hours. If you want to baby the battery as much as possible, combine this with “Optimized Charging” or “Adaptive Charging” (see below). For everyone else: the following tips give you more bang for your buck.

Avoid heat. This is the single most important point. Don’t leave your phone in a sun-soaked car. Don’t put it directly on the dashboard. Don’t leave it under your pillow while charging. While gaming or running GPS navigation, take a break when the device gets really warm. A lot of people leave their phone baking in the sun by the pool in summer — and then wonder why the battery wears out so fast.

Turn on optimized charging. Both iOS and Android can do this. On the iPhone it’s called “Optimized Battery Charging”; on many Android devices it’s “Adaptive Charging” or something similar. The idea is simple: the device learns when you typically unplug it and only tops up the last few percent shortly before that. So if you charge overnight, the battery sits at 80% for hours after midnight, and the remaining 20% only gets topped up around six in the morning. This single setting is the single most effective measure — and hardly anyone actively turns it on.

Clean up background refresh. Lots of apps update themselves in the background, even ones you never open. That eats battery and data. In settings, you can decide app by app whether that’s necessary. On the iPhone, look under “General → Background App Refresh”; on Android it’s tucked away differently depending on the manufacturer. Going through the list once and turning it off for unimportant apps makes a noticeable difference.

Display brightness and always-on display. The display is the biggest power consumer in your phone. Letting brightness adjust automatically and turning off the always-on display (if your device even has one) noticeably extends runtime. On OLED displays, feel free to use dark mode — black pixels are genuinely off and don’t consume power.

What you can realistically expect

Here’s the honest message: even if you do everything right, after two to three years you’ll have a battery at about 80% of its original capacity. That’s not a defect, it’s physics. Lithium-ion batteries age even when they’re not being used. They are wear parts, just like the tires on your car.

80% sounds like a lot at first, but you’ll notice it in daily use: the device that used to comfortably last until evening now asks for an outlet in the afternoon. Once capacity drops below 70 to 80%, you’ll feel it.

On the iPhone you can check this easily: Settings → Battery → Battery Health. It shows you the current maximum capacity as a percentage. On Android devices, sadly, it’s all over the map. Some manufacturers show it in settings under “Battery” or “Device Care.” On many devices you have to dig deeper or use diagnostic codes. Apps like AccuBattery can estimate the value over several charge cycles, but they’re not as accurate as the manufacturer’s own readout.

If capacity drops below 70% and the device is otherwise still working well, a battery replacement can be worthwhile. Many manufacturers offer this service themselves, often at reasonable prices. On some models it’s difficult or impossible without damaging the device — in which case a battery swap is often the beginning of the end, because the repair becomes almost as expensive as a new device.

Bottom line: no drama, just a few good habits

Smartphone batteries are wear parts. They age, and you can’t prevent that. But you can slow their decline — with surprisingly simple measures:

• Turn on “Optimized Charging” or “Adaptive Charging”
• Avoid heat like the plague
• Turn off background refresh for unimportant apps
• Tame display brightness, disable the always-on display
• If you really want to baby it: also keep the battery between 20 and 80%

What you can skip: deliberately draining the battery, using only original chargers, installing shady battery apps, or — heaven forbid — putting your phone in the fridge. The technology has moved on; the old rules no longer apply.

And when the battery noticeably weakens after three years? That’s not a failure of technology, and it’s not a sign that you did anything wrong. That’s simply the reality of lithium-ion batteries. A replacement is often cheaper than you’d think — and in many cases the more sustainable solution compared to buying a new device right away.

Which battery myths have you heard? What do you do yourself to take care of your battery — and what turned out to be useless? Let us know in the comments.