Laptop batteries: Why don't they maintain ~50% charge? (Can they be made to?)

[jchpmn]

Knowing that device batteries are at their points of worst stress when at either 0% or 100% capacity, I tend to only charge my phones to about 70% and run them down to about 30%, when I can. But then I look at my laptop, which is virtually always plugged in. That means the battery stays at 100% constantly, presumably the worst thing I could possibly be doing to it.

 

So why don't laptop manufacturers offer a default regulation of battery at around 50% while attached to mains electricity and then an option to override and charge to the full 100% when required? 

 

Does 3rd-party software already exist that can achieve this?

[WereCatf]

7 minutes ago, jchpmn said:

So why don't laptop manufacturers offer a default regulation of battery at around 50% while attached to mains electricity and then an option to override and charge to the full 100% when required?

Some manufacturers do, like e.g. MSI does allow you to limit the maximum your battery will charge to on some of their laptops. I know some other manufacturers do as well, but I don't know which ones.

8 minutes ago, jchpmn said:

Does 3rd-party software already exist that can achieve this?

I don't think so. At least I've never seen or heard of such software.

[Eigenvektor]

This wouldn't really improve things. All batteries slowly discharge over time, so to stay at 50% you'd still be constantly discharging/recharging the battery once its charge goes outside some acceptable limit to go back to 50%.

 

It's also not 100% certain what 50% means. Does it mean all cells of the battery stay at 50% charge, or does it mean that 50% of the battery's cells stay at 100% charge while the remaining cells stay discharged? A (deeply) discharged cell is one of the most destructive things you can do for a battery. But to increase it's lifespan you also wouldn't want to keep recharging all cells constantly to stay around 50%.

[WereCatf]

3 minutes ago, Eigenvektor said:

This wouldn't really improve things. All batteries slowly discharge over time, so to stay at 50% you'd still be constantly discharging/recharging the battery once its charge goes outside some acceptable limit to go back to 50%.

Um, the laptop would obviously charge the battery up to the limit every time it dropped, so... Also, no, li-ion and similar cells do not discharge fast enough for it to matter. I have a box full of 18650 cells and they all still have the same voltage as they did years ago when I got them, for example. It's easy for a li-ion cell to maintain its charge for a decade straight.

3 minutes ago, Eigenvektor said:

or does it mean that 50% of the battery's cells stay at 100% charge while the remaining cells stay discharged?

That wouldn't work. The battery would be unuseable, if some cells were empty, so no, that's not how it works. There is a cell-balancing circuit in laptop-batteries.

[Jeppes]

Hysteresis. Charge till 60%, stop, start charging again when 40%. Should be easy enough.

 

My guess would be that they want people to kill batteries so that they can sell new stuff once per 2-3 years instead of 5.

[Tegneren]

27 minutes ago, WereCatf said:

Some manufacturers do, like e.g. MSI does allow you to limit the maximum your battery will charge to on some of their laptops. I know some other manufacturers do as well, but I don't know which ones.

I don't think so. At least I've never seen or heard of such software.

Lenovo has this feature in the Lenovo Vantage software, it limits the battery at 60% on my laptop. But I doubt that will work for other brands

[Eigenvektor]

23 minutes ago, WereCatf said:

Um, the laptop would obviously charge the battery up to the limit every time it dropped, so... Also, no, li-ion and similar cells do not discharge fast enough for it to matter. I have a box full of 18650 cells and they all still have the same voltage as they did years ago when I got them, for example. It's easy for a li-ion cell to maintain its charge for a decade straight.

That assumes the laptop does not use the battery in any way while plugged in, so it can retain its charge. Not sure this truly works while the battery is physically connected to a circuit?

 

23 minutes ago, WereCatf said:

That wouldn't work. The battery would be unuseable, if some cells were empty, so no, that's not how it works. There is a cell-balancing circuit in laptop-batteries.

I stand corrected.

[WereCatf]

4 minutes ago, Jeppes said:

My guess would be that they want people to kill batteries so that they can sell new stuff once per 2-3 years instead of 5.

Dead batteries in gaming-laptops don't really cause people to buy new laptops, since those laptops are plugged into the wall most of the time anyways. In non-gaming-laptops it might be a different matter.

[WereCatf]

Just now, Eigenvektor said:

That assumes the laptop does not use the battery in any way while plugged in, so it can retain its charge. Not sure this truly works while the battery is physically connected to a circuit?

You do know that it's possible to e.g. disconnect the battery from the circuit when there's another power-source -- that is, the charger -- plugged in? All you really need is a MOSFET, a diode and resistor to do that, or you can implement more fancy logic with a dedicated chip.

[jchpmn]

Thanks for the illuminating answers, and it's good to know that at least a couple of manufacturers are looking at this.

[WereCatf]

7 minutes ago, Tegneren said:

Lenovo has this feature in the Lenovo Vantage software

I have a vague image of Dell allowing this as well on some models, but that's a very vague image, so could be I just remember wrong. And I'm too lazy to bother Googling about this topic

[Eigenvektor]

9 minutes ago, WereCatf said:

You do know that it's possible to e.g. disconnect the battery from the circuit when there's another power-source -- that is, the charger -- plugged in? All you really need is a MOSFET, a diode and resistor to do that, or you can implement more fancy logic with a dedicated chip.

True, but that requires hardware support, which is why I guess you need explicit support by the manufacturer for this feature. I also know that some laptops under high load will drain the battery even when plugged in, apparently because the charger is underpowered.

[WereCatf]

18 minutes ago, Eigenvektor said:

True, but that requires hardware support, which is why I guess you need explicit support by the manufacturer for this feature. I also know that some laptops under high load will drain the battery even when plugged in, apparently because the charger is underpowered.

As the saying goes, there's more than one way to skin a cat.