In relation to Does recharging a battery when it is only half-way dead decrease its life span? I read an article about Maximizing the lifespan of a laptop battery where Samsung puts it:

Most battery damage occurs when the cells inside are at or near capacity. That’s because batteries get a bit hot under the collar when they max out their charge at 100 percent. This heat causes the delicate structures within to start to break down, which ultimately makes the battery less capable of holding a charge. Eventually capacity drops to the point where the battery won’t hold a charge at all and it has to be replaced.

They offer a solution which suggests to:

[...][cap] the charge at 80 percent.

To what extent is this true?

And although not directly related, I figure it must matter in this relation that electric cars are charged to 80% when performing quick charging.

  • Interesting, AFAIK, the standard claim that Li-Ion batteries should be fully charged to prolong their lifespan.
    – vartec
    Oct 8, 2012 at 10:33
  • @vartec Can you provide a reference to someone making that claim?
    – Aske B.
    Oct 8, 2012 at 10:43
  • 2
    "electric cars are charged to 80%" - could that be because charging is nonlinear? E.g. charging from 20% to 80% is fast, but 80% to 100% takes longer (per percentage point)? Oct 8, 2012 at 12:01
  • @Piskvor Maybe, but about charging electric cars, the method of speed charging to 80% seems to be for safety of the battery. "A communications link incorporated into the charging cord allows the car's battery management system to control the rate of charge to avoid damage to the battery. The system will, for example, slow down charging if the battery overheats or will typically stop charging when it reaches 80 percent of capacity." (source). I figure that if charging the battery above 80% is bad in cars, it could also be bad on a smaller scale.
    – Aske B.
    Oct 8, 2012 at 12:54
  • @RoryAlsop You're right. It's entirely possible to charge batteries in cars above 80%, but from the article I just quoted they say "The system will [...] slow down charging if the battery overheats or will typically stop charging when it reaches 80 percent of capacity", so even if the capacity was 70% before charging, it will stop doing fast charging at 80%. What I'm saying is there must be some reasoning behind this security measure that could be linked to batteries of laptops.
    – Aske B.
    Oct 8, 2012 at 14:11

2 Answers 2


Interestingly, despite my comment above (which was based on some info I had on early laptop batteries) I have found this article on batteryuniversity.com on Lithium based batteries. I would definitely recommend reading it, and the other information pages there – a lot of good into on the different types:

This table compares the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent.

Depth of discharge Discharge cycles
100% DoD 300-500
50% DoD 1,200 - 1,500
25% DoD 2,000-2,500
10% DoD 3,750-4,700

Cycle life as a function of depth of discharge:
A partial discharge reduces stress and prolongs battery life. Elevated temperature and high currents also affect cycle life.

This table summarizes variation due to charge level.

Charge level (V/cell) Discharge cycles Capacity at full charge
[4.30] [150-250] [110%]
4.20 300-500 100%
4.10 600-1,000 90%
4.00 1,200-2,000 70%
3.92 2,400-4,000 50%

Discharge cycles and capacity as a function of charge:
Every 0.1V drop below 4.20V/cell doubles the cycle; the retained capacity drops accordingly. Raising the voltage above 4.20V/cell stresses the battery and compromises safety

This figure demonstrates cycle count as a function of charge voltage. At 4.35V, the cycle count is cut in half.

Effects on cycle life at elevated charge voltages: Higher charge voltages boost capacity but lowers cycle life and compromises safety

Conclusion: 80% may well be the sweet spot, as over-charging causes damage and under-charging reduces effective capacity.

  • 2
    So what do you conclude from this data? Dec 22, 2017 at 0:40
  • 1
    It's worth noting that an increasing number of phones and BIOSes have an option to change the "max charge" setting to less than 100% for this reason. My laptop and phone are both using this feature. Dec 14, 2023 at 19:23

As reported in Apple: iPad Battery Nothing to Get Charged Up About, the device showing "100%" does not mean that the battery is actually fully charged.

So here’s how things work: Apple does, in fact, display the iPad (and iPhone and iPod Touch) as 100 percent charged just before a device reaches a completely charged state. At that point, it will continue charging to 100 percent, then discharge a bit and charge back up to 100 percent, repeating that process until the device is unplugged.

Apparently, "just before" is around 90% charge.

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