Laptop's Batteries Auto-disconnect?

[MoemenShahawy]

I am about to buy one of those 2 laptops

Dell 15-5558 or the Acer E5-571G and I heard some time last week that there's some laptops that -when connected to the AC charger- automatically disconnect once the battery is fully charged even if it's still plugged in so it wouldn't harm the battery, unfortunately none of the laptops' specs (or any other for that matter) mention such feature, so anyone knows if one of those 2 includes it?

 

[unreal9400]

Yes, it will stop charging the battery once it hits 100%.
You can leave the battery on the laptop and it won't do any harm.

 

[MoemenShahawy]

Yes, it will stop charging the battery once it hits 100%.
You can leave the battery on the laptop and it won't do any harm.

Both, the dell and the acer?

 

[unreal9400]

Most modern laptops will stop charging once it is fully charged.
If you are plugged in most of the time or gaming you might want to unplug the battery to prevent it from getting warm which may damage it in the long run.
Other than that, there's no harm done to the battery since there is controller inside your laptop that will control circuit to prevent from overcharging once the battery is full.
Go with the acer since it has longer battery life compared to dell.

 

[Solandri]

Charging a battery to 100% or discharging it to 0% damages the battery, decreasing its capacity as it ages. This is the reason some of the batteries on older laptops only last 5 minutes.

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

I've seen two strategies used by manufacturers to avoid this damage. The first is the one you mention - stop charging when it hits 100%, and don't recharge it until it drops to 90% or 95%. Probably the worst thing you could do to the battery was immediately top it off to 100% again the moment it dropped to 99%. The old Toshiba laptops were pretty bad about this, topping off the battery every few minutes. Most of those Toshiba batteries needed to be replaced within a year. Back in those days, we would remove the battery from the laptop once it was fully charged, and insert it only when we needed to use it without AC power.

The second method is to understate the battery's capacity. That is, the label on the battery will say 48 Wh, but Windows will detect it as a 43 Wh battery. The extra 10% is used to provide a buffer at the high and low ends. That is, when Windows reports the battery is charged to 100%, it's actually only charged to 95%. When it reports the battery is at 0%, it's actually at 5%. Sometimes this is accomplished by tricking Windows into thinking it's a 43 Wh battery. Sometimes it's done by telling Windows the battery is already worn and only has 43 Wh of capacity left. This is the same strategy employed by electric and hybrid cars. Most of them limit battery charges to the middle 50%-60% of the battery's actual capacity.

Every modern laptop I've seen uses one of these strategies to protect battery longevity. I think in the past manufacturers abused this as a way to increase sales of replacement batteries. But with the move towards internal batteries, I think they are now more interested in making sure the battery works well for many years.