Maximizing battery total life span

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bentout12

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I am using a Dell XPS 9550 primarily as a desktop. By that, I mean, it is pretty much always plugged in and I rarely need to move it. In order to keep from totally burning out the battery, I have completely pulled the battery out and just use the laptop on AC power. When I need to travel, I'll put the battery in. With the number of screws needed to do this every time, it is super inconvenient, so I wanted to know if there was a better alternative.

The BIOS battery options include a "Primarily AC Use" setting that says it is for users who mainly use the laptop plugged in. Does anyone know how this actually works? If I am on AC power with the battery charging and it hits 100%, what happens to the battery if I continue to leave the thing plugged in for an extended session, say 6 hours? Is it just constantly running down to 99% and then charging back up to 100%? And how does the AC Use option change this?

It would be nice if there was simply a way to disable battery charging completely without pulling the thing out, but if there is some good alternative, i would love to hear about it.

Thanks!
 
According to this thread, it limits the battery's max charge to 96%. That is, the computer rescales the battery charge so when Windows reports 100% and stops charging, the battery is actually at 96%. Thus preventing it from being charged the final 4%.

http://forum.notebookreview.com/threads/dell-xps-13-2015-broadwell-infinity-display-owners-thread.769261/page-191

That's good. Probably not as good as 90% or 80%. But the deeper the charge/discharge, the more damage you do to Li-ion batteries. So 96% is better than 100%.

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

I've heard of people hacking their laptops to install a switch to the power lead going to the battery. That way you can disconnect it without having to open up the case. That's kind of extreme though. You can get replacement batteries for most major laptop brands even though the batteries aren't designed to be user-replaceable. And even if you take good care of the battery it'll probably need replacing anyway in 5-7 years.
 

bentout12

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Jun 13, 2015
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Thanks for that. Sounds like it's not nearly as good as just pulling the damn thing out either. I found a different option in the bios that basically lets me set a maximum and minimum charge percentage. What do you think of that? What I've set it to is to only charge up to 90% and then only discharge down to 50%. Does that mean I can just leave it plugged in and once it hits 90% it will just stop using the battery entirely? If that is true and I never unplug it, that seems like it would basically be the same as pulling it out of the computer, since the computer won't be drawing any power on it. Obviously, if I do unplug it to move around like a more traditional laptop, it would then be drawing power, but that happens so rarely it wouldn't be an issue.


UPDATE: I've had it set to maximum 90%, minimum 50% all night and let it run on battery just a bit to drain it down a little bit and see what happens. I plugged it back in at 83% and have been using it on AC power all night. The battery is still at 83%. Is it safe to say this is roughly the same as just removing it since it appears not to be getting used at all? I know it will eventually hit 50% and charge again, but my guess is that would take an extremely long time if I never unplugged it.




 

jaguarskx

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If you look down at the right corner of the task bar you should see the battery icon. Right click and you should see something called Dell Power Manager Lite. That allows you to control battery charging. I think there are 3 or 4 options.

If you do not see then you can download it from the following link:

http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=4T7MN&fileId=3581947779&osCode=WT64A&productCode=xps-15-9550-laptop&languageCode=en&categoryId=UT

It should give you 3 or 4 options for charging your battery. Two are as follows:

- Primarily AC Use
- Custom


I have the Dell Inspiron 15 7559 (a recent purchase) and I use the Custom option. The minimum charge is 50% and cannot be set any lower than that. The maximum charge can be from 50% to 100%. I set it to stop charging at 60% for testing purposes last night. I allowed the battery to drop to around 25% to 30% several times and then plugged in the charger. The laptop always stops charging at 60% so unless that little app and Window's battery monitor are both lying to me, I trust that the battery actually does stop charging at 60%. I assume when the battery drops down to 50% or less (since batteries naturally self discharge over time), that the laptop will charge the battery again until it reaches 60%.
 

Based on your update, I think what you have is a "don't recharge until" point. That is, the way you have it set up:

- The battery will not start to recharge until it hits 50%.
- The battery will stop charging at 90%

So basically if you leave it plugged in all the time, it'll bounce between 90% and 50%. It'll charge to 90%, then the laptop won't send any current to the battery. The battery will slowly self-discharge. The laptop will let it self-discharge until it hits 50%, at which point it will charge it up to 90% again.

90% is still a little high IMHO. Unless you plan to use the laptop on battery frequently (so you want a little more charge if you suddenly decide to unplug it and go), I'd probably set it at 80% as the high.

50% as a recharge point is very aggressive IMHO. Li-ion batteries simply don't self-discharge that quickly. I'd probably set it at about 10% lower than the stop charge level. So if you're stopping charging at 80%, I'd set the recharge point to 70%. That'll probably limit it to about one recharge a week due to self-discharge. If you frequently unplug the laptop for short periods (e.g. you take it between home and work but use it on AC in both places), then you might experience more discharge on a daily basis, and 60% or 50% might be warranted.
 

bentout12

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Jun 13, 2015
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This is super helpful, thanks. Just a few other questions:

When you say 50% is aggressive, do you mean that I'm going below the optimal discharge level to maximize the battery's condition as long as possible? For example, I know letting it discharge to 0 is pretty much always very hard on it. So, is the 70% you recommended closer to the ideal?

Second - and I think I already know based on what you've said - would it be essentially correct to say that the battery is completely not in use when it is in that "not charging window" kind of in the same way as if I had pulled it out of the computer? That's really what I'm trying to achieve, so if this gets me there, then it's a very good happy medium.

Again, thanks for the super great info.



 
50% is "aggressive" in that (1) it's probably safe to go a lot lower than 50%. Most electric vehicle manufacturers are using their Li-ion batteries in the 20% to 80% range. And (2) it'll probably take the battery a few days to more than a week to self-discharge from 90% to 80%, Self-discharging to 50% would probably take forever.

So if your interest is in using the battery as little as possible, you can probably go a lot lower than 50%. If your interest is in just charging the battery infrequently, then 80% or 70% won't be much worse than 50%. (Assuming 1% a day, 80% results in 36 additional partial charge cycles per year, 70% results in 18/yr. 50% results in 9/yr. There just isn't much practical difference between these numbers of cycles per year in terms of battery longevity, which is typically 300-1000 cycles.)

Yes your battery is not in use when it's in the "not charging" window. The system is still measuring its voltage occasionally and it'll switch over instantly if the AC power cord falls out. But yes, essentially it's the same as removing the battery. The biggest caveat though is that Li-ion batteries do not respond well to being stored at high temperatures. So if you game or run at 100% CPU a lot on this laptop, that could expose the battery to constant higher temps which could degrade it even though you're not putting cycles on it. In that case, removing the battery would be better.
 

bentout12

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Jun 13, 2015
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That's fantastic, thanks so much for elaborating. I think I'll experiment with different thresholds to see what ends up being the most useful. With the rarity of how often I end up unplugging, I think a lower minimum charge might be better, but it sounds like 50% is probably lower than anyone would ever need. Thanks!



 
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