For battery life, stopping around 80% is better: a lithium-ion battery is under less stress at a lower charge voltage and lasts more cycles. Charging to 100% is fine when you need the full runtime, as long as the phone does not stay full for hours, especially when it is warm.
The "80% rule" is everywhere: in phone settings, in forums, in videos. Charge to 80%, never to 100%, and your battery will last longer. It is true, but it is not the whole story. Stopping at 80% costs you runtime every day, and whether it is worth it depends on how you use your phone.
Why does charging to 100% wear the battery more?
A lithium-ion battery reaches its highest voltage when it is full. For a standard lithium-ion cell, Battery University gives a ceiling of 4.20 volts, and explains that a high voltage stresses the battery. It even states that it is better not to charge lithium-ion fully, and that lowering the voltage threshold prolongs battery life, at the price of less runtime.
Its figures show the trade-off clearly:
| Charge voltage per cell | Approximate charge reached | Discharge cycles |
|---|---|---|
| 4.20 V | 100% | 300 to 500 |
| 4.10 V | about 90% | 600 to 1,000 |
| 4.00 V | about 73% | 850 to 1,500 |
| 3.92 V | about 65% | 1,200 to 2,000 |
The percentages are the capacity each voltage gives compared with a full 4.20 V charge. In other words, giving up a little runtime at the top can multiply the number of cycles. Stopping around 80% sits between the 4.10 V and 4.00 V rows: noticeably more cycles, at the cost of part of the charge.
Does it matter how low you let the battery go?
Yes. The other half of the rule is the bottom of the charge. Battery University gives the number of cycles a typical lithium-ion (NMC) cell delivers depending on how deeply it is discharged each time:
| Depth of discharge | Approximate cycles (NMC) |
|---|---|
| 100% | 300 |
| 80% | 400 |
| 60% | 600 |
| 40% | 1,000 |
| 20% | 2,000 |
| 10% | 6,000 |
So the deep cycle from 100% down to nearly 0% is the hardest on the battery. Lithium-ion has no memory effect: Battery University stresses that partial discharges are fine and that the battery does not need periodic full cycles. Plugging in at 30% or 40% is perfectly normal.
And what about heat and time at 100%?
The two effects add up. A full battery that is also warm ages faster. In Battery University's storage tests, a battery kept for a year at 25°C held about 96% of its capacity at a 40% charge, but only about 80% at 100%. At 40°C the figures drop to 85% and 65%. It also warns that keeping the battery full for a long time, especially when hot, can be more stressful than cycling.
This is why the 80% rule matters most for phones that stay on the charger for hours: overnight, on a desk all day, or in a car mount.
What do Google, Samsung and Apple recommend?
All three now offer a way to stop below 100%:
| Phone | Setting | Behaviour |
|---|---|---|
| Google Pixel | Limit to 80% | Stops at 80%; Google suggests it if you usually end the day with charge left |
| Google Pixel | Adaptive Charging | Charges to 100% just before you usually unplug, so the phone is not at 100% for long |
| Samsung Galaxy (One UI 6.1) | Battery protection: Maximum | Stops charging at 80% |
| Samsung Galaxy (One UI 6.1) | Battery protection: Adaptive | Holds the maximum protection during sleep, then fills up about an hour before you wake |
| Samsung Galaxy (older One UI) | Protect battery | Caps the charge at 85% |
| iPhone | Charge Limit | Lets you choose a limit from 80% to 100% in 5% steps |
Apple adds a detail worth knowing: with a limit below 100%, the iPhone occasionally charges to 100% anyway, to keep its battery level estimate accurate. Google also notes that keeping the battery at 100% for a long time can strain it over the long term.
So should you charge to 80% or 100%?
It depends on your day:
- You end most days with charge left: turn on the 80% limit (or 85% on older Samsung phones). You lose a little runtime you were not using anyway, and the battery ages more slowly.
- You charge overnight but need a full battery in the morning: use adaptive charging. The phone holds back the charge during the night and finishes it shortly before you usually unplug.
- You have a long day ahead, a trip, a shift: charge to 100%. That is what the battery is for. Just unplug soon after it is full.
- The phone often drops very low: charge more often, in short sessions, rather than draining it to 0% and refilling it to 100%.
The goal is not a perfect number. It is to avoid the two extremes, long hours at 100% and deep drops towards 0%, especially when the phone is hot.
How can you follow your own charging habits?
Settings tell the phone what to do; they do not show you what really happened. The Maqbis app shows it. On the battery page you see the battery level on a gauge and a chart of the level over the last 24 hours, so you can see how high you charge and how low you go.
When the battery reaches 100%, the app sends an alert telling you to unplug to preserve battery health, and it notes when the phone stayed on the charger long after it was full. If your phone stops charging before 100% because a charge limit is on, the battery page shows the level at which charging stops. The temperature of the battery is shown too, with an alert if it gets too high.
The app does not set the limit for you, and it does not change how your phone charges. It gives you the information to choose the habit that suits you.
The short answer
80% is better for battery life, 100% is better for runtime. Use a charge limit or adaptive charging if your day allows it, charge to 100% when you need it, avoid hours at full charge and deep drops to 0%, and keep the phone cool. That is enough to get the most out of your battery.
Frequently asked questions
Is it bad to charge my phone to 100% every time?
It is not dangerous, but it ages the battery faster than stopping lower, mainly when the phone then stays at 100% for hours or gets warm. If you unplug soon after it is full and use the charge, the cost is small.
Should I let my battery drop to 0% before charging?
No. Lithium-ion has no memory effect and does not need full cycles. In Battery University's figures, shallow discharges give far more cycles than full ones.
Why does my iPhone sometimes charge to 100% with an 80% limit?
Apple explains that with a charge limit below 100%, the iPhone occasionally charges to 100% to keep its battery level estimate accurate.
Is 80% enough for a full day?
It depends on your phone and your use. Google recommends its 80% limit if you usually end the day with charge left. If you often run low, charge to 100% on those days.
