Li-ion battery : Connected to AC at 100% vs. Charging 35%-75%.

Lordofdeath123 · 20 May 2017 at 14:36

Hi all.

I had a question about battery care. I know neither is ideal, but, of these two, which one is better?

1. Constantly having the Laptop connected to the AC at 100%
2. Charging to 75%, using on battery till its on 35%, than charging to 75% again etc.

Ignoring the impracticality of the second option, which one wears out the battery less?

Note that the battery is not removable, so charging to 50% and removing it is sadly not an option. Also, the Laptop (which is an Acer) has no inbuild power manager, that can cap the charge to 75%, and only keep charging up once it hits 35% (of natural discharge!, rather then discharge through battery usage).

As such, I am kinda in a situation where I have to choose between 1. or 2. I should also mention that I do not know when the laptop will start recharging, at 99% or 95%. I hope for the latter, but fear the former might be closer to the truth, since the Laptop really seems to lack any kind of battery management.

Cheers.

Rroff · 20 May 2017 at 14:44

Depends a bit on the charger and controller - Li-ion should stop charging once the battery is "full" unlike older battery tech that would continue trickle charging - some controllers will not draw from the battery while plugged into AC.

Li-ion batteries tend to have a fairly limited number of charge cycles so generally I think its better to keep them topped up than cycling.

Anecdotally I've a variety of devices that use Li-ion batteries some that are plugged in at 100% constantly and others left until they almost run down then charged up again and there doesn't really seem to be much in it when it comes to how well the battery performs when they are running on battery or how long the batteries last before they need replacing - unless one has excessive number of cycles which tends to kill them sooner.

Lordofdeath123 · 20 May 2017 at 14:52

some controllers will not draw from the battery while plugged into AC.

I am pretty sure that this feature exists on this laptop, as well as on most semi-modern ones. The thing though is this, the battery naturally discharges to 99%, and fairly fast too. (Much fast than say 50-49%). At this stage, `some' (I am not sure if this laptop does or not, I asked on their forum: no replay), laptops recharge immediately. Hence, it could be recharging 99-100 all the time, which is apparently fairly bad. Much worse than 49-50%. But, since it is still discharging much slower than when used, I am not sure which is worse.

I do tend to agree with you though... Bloody integrated batteries and bloody `planned obsolescence '.

Cheers.

Rroff · 20 May 2017 at 14:56

I see that behaviour on my DIY power bank

the output doesn't draw from the battery while there is an external charge source connected but after a couple of days or so the batteries naturally discharge to "99%" and then the charging kicks in again - it isn't particularly good for the battery but I don't think its any different to other partial charge cycles - the documentation on the charge controller recommends doing a full cycle every 4 months to offset any detrimental effect on the battery but no idea if that is sound scientifically or not.

Lordofdeath123 · 20 May 2017 at 15:15

Fair enough. I was given to understand that typical laptop batteries discharge to 99% often in a few minutes. So, having it go 99-100, 100-99 10 times an hour seemed also quite stressful. I am kinda sad that with about 5 gazzillion articles about battery care, no one actually writes anything more than a copy-pasted sequence about what a discharge cycle is and than the three standard tips that one should not always let it go to 0%, that one should not throw it down a volcano, like the one ring, and that one should discharge to 50% before disconnecting it, when not used...

Oh well... I guess I will just use the AC whenever possible and watch on HWinfo what the wear level is. If it goes down too fast, I will try to keep it 35-75% for a week and see what that does... Ultimately, I will just learn how to replace the battery cells, hehe. That seems cheaper.

Thanks for the replays mate.
Cheers.

Rroff · 20 May 2017 at 15:50

Yeah the documentation on these kind of things can be frustrating

often contradictory and never goes into any real detail.

Lordofdeath123 · 20 May 2017 at 16:00

Rroff said:
Yeah the documentation on these kind of things can be frustrating often contradictory and never goes into any real detail.

So very true