Li-Ion batteries and charging on modern laptops

Yuki Core

Honorable
Aug 1, 2013
25
0
10,590
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I'm in possession of HP Spectre x360, and I have been wondering.

If I were to leave it charging while it's at 100%, would it still use power from the battery (thus slowly ruining it) or it would use the power plug for power?
 

jaguarskx

Champion
Moderator
When a laptop's battery is fully charged, the laptop switches from the AC charger to the battery. When the battery's capacity drops down to 95% or so it switches back to the AC charger.

Empirical evidence has shown that when a battery is close to it's full charge there is a chemical reaction that takes place that forms "lithium ion plates" in the laptop's battery. Basically the closer the battery is near it's maximum capacity the more likely this chemical reaction will take place. What happens is lithium ions starts to combine with each to form plates. When this happens the battery capacity starts to decrease because those lithium ions can no longer hold a charge. The more lithium ion plates there are the lower the battery capacity will be.

Generally it is bad to fully charge a laptop's battery. When Windows 7 was the most current OS, some laptop brands like Dell and Lenovo provided custom power management programs that would basically tell Windows to stop charging the battery once it reaches something like 60% - 80% depending on the brand. You can manually override it to fully charge the battery if you were going to use it away from an AC outlet. However, Windows 8 and Windows 10 do not support those types of power management programs.

From what I have read (which has not been confirmed) some laptop brands install batteries with higher than advertised battery capacity and the laptops are designed to only charge the battery up to the advertised capacity to help prolong the life of the battery. For example, the HP Spectre x360 is advertised as having a 56WHr battery. The actual capacity could be 66WHr, but the laptop will only charge it to "56WHr", that means whenever Windows tells you the battery is fully charged, in actuality it is only at about 85% of the battery's true maximum charge. Again, this is just speculation and has not been confirmed to the best of my knowledge.
 

glamdringfh

Honorable
Dec 23, 2013
41
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10,610
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The short answer is yes, leaving your laptop plugged into main power while the battery is fully charged will reduce the batteries capacity to hold a charge. The laptop doesn't route power around the battery when it is full, and when the battery is running consistently at full charge it causes the battery to chemically kill it’s self.

In order to squeeze as much life out of your lithium-polymer battery, once your laptop hits 100 percent, unplug it.

Great article on the matter if you feel like reading some specific details on battery health: http://thisweekinbatteries.blogspot.com/2010/02/pull-plug-your-battery-will-thank-you.html
 

jaguarskx

Champion
Moderator
When a laptop's battery is fully charged, the laptop switches from the AC charger to the battery. When the battery's capacity drops down to 95% or so it switches back to the AC charger.

Empirical evidence has shown that when a battery is close to it's full charge there is a chemical reaction that takes place that forms "lithium ion plates" in the laptop's battery. Basically the closer the battery is near it's maximum capacity the more likely this chemical reaction will take place. What happens is lithium ions starts to combine with each to form plates. When this happens the battery capacity starts to decrease because those lithium ions can no longer hold a charge. The more lithium ion plates there are the lower the battery capacity will be.

Generally it is bad to fully charge a laptop's battery. When Windows 7 was the most current OS, some laptop brands like Dell and Lenovo provided custom power management programs that would basically tell Windows to stop charging the battery once it reaches something like 60% - 80% depending on the brand. You can manually override it to fully charge the battery if you were going to use it away from an AC outlet. However, Windows 8 and Windows 10 do not support those types of power management programs.

From what I have read (which has not been confirmed) some laptop brands install batteries with higher than advertised battery capacity and the laptops are designed to only charge the battery up to the advertised capacity to help prolong the life of the battery. For example, the HP Spectre x360 is advertised as having a 56WHr battery. The actual capacity could be 66WHr, but the laptop will only charge it to "56WHr", that means whenever Windows tells you the battery is fully charged, in actuality it is only at about 85% of the battery's true maximum charge. Again, this is just speculation and has not been confirmed to the best of my knowledge.
 


The last 3 laptops I have purchased have charged the battery to 100%, then switched to just using the ac adapter. Once the battery lost charge from not being used, which all batteries slowly do, down to 95%, the charger would kick back in and top it off again. This cycle happened perhaps once every 2-3 weeks. This removed a lot of wear on the battery by not constantly applying a trickle charge to keep the battery topped at 100%. Of course, this does nothing to address "lithium ion plates" forming, though. My current battery shows a wear level of 4%, after 8 months, and my laptop is plugged in 24/7.

 
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