[Lifehacker article] How often should you fully discharge?

[theilluminati]

http://lifehacker.com/5875162/how-often-should-i-charge-my-gadgets-battery-to-prolong-its-lifespan

The article says once a month. But should you fully discharge once a month

• your phone which you charge daily (from 50%, see the article)
• your MP3 player which you charge weekly (from 50%, see the article)
• your Kindle which you charge monthly anyways

Respectively? More guidance on that?

 

[markr6]

I have a 5200mAh external battery pack for my phone. The manual says to charge/discharge every week, or at the very least once each month. It also says to keep it stored around 50% when not in use. Sounds right to me! It's nice to see this kind of info in a manual to inform those not on CPF :)

Personally I'm not sold on the FULL discharge part, but my external battery pack always gets there a few times each year when I'm using it while backpacking.

Looking forward to some more detailed feedback...

 

[Wrend]

From what I understand, the only reason someone might want to fully discharge Li-Ion and Li-Po type cells (hopefully ones not in series) is to maybe recalibrate battery meters. Not exactly sure why, but I've heard this rationale. Seems as though they should be able to measure this based on voltage levels, but then, maybe this helps to provide an updated usable voltage range for some "smart" devices to work with.

Anyway, no, for the sake of the cells them self, you don't really need to fully discharge these types of cells, and leaving them fully discharged for extended periods of time will more than likely damage them significantly. In modern "smart" devices with battery circuits built-in, I would hope they turn themselves off before this happens, and that maybe "0%" is really 10% remaining capacity. I'm not sure about that though.

My main advice for general practice is: Try to avoid discharging below 20% remaining capacity before you recharge, and especially don't leave the cell fully discharged, if you can help it.

More fully discharging once in a while isn't likely to do any significant damage to the cells at least, so long as they're not left fully discharged for any extended period of time.

Storing at 50% charge for longer periods of time is also likely a somewhat beneficial practice, if you need to store them away for a bit, but try to make sure they don't self-discharge (either from internal circuitry drain, or just capacity loss over time) too much below this.

Again, this is only specifically for Li-Ion and Li-Po type cells. These kinds of cells aren't helped much (if at all) in the same way that more fully cycling NiCd and NiMH cells can help them maintain higher performance over their cycle life expectancy (as well as not being left slow roasting on a trickle charger after they're fully charged, as was and is unfortunately sometimes common practice).

 

[RetroTechie]

From what I understand, the only reason someone might want to fully discharge Li-Ion and Li-Po type cells (hopefully ones not in series) is to maybe recalibrate battery meters. Not exactly sure why, but I've heard this rationale.

If you know battery capacity ('historical records'), a previous State-of-Charge (for example: empty), and know at what rate you have been charging (= measured), then you can calculate remaining charge, time until empty, time until full, etc.

For a battery with unkown capacity that doesn't work. Capacity as new is of little use since batteries degrade, so their actual capacity is always changing.

So the point of a full discharge is to measure actual capacity, and have a known SoC point as reference. Personally I don't see the point to do this regularly, unless you feel it is critical to have an accurate % shown. Batteries will run empty from time to time, when it happens you have your up-to-date capacity info then. And when a battery is about to run empty, that's usually pretty clear even if remaining charge was estimated wrong.

Seems as though they should be able to measure this based on voltage levels,

Seems like a good idea. But I suspect not accurate enough (perhaps because exact voltages may depend on temperature, etc). More useful where accurate charge estimate isn't important (mp3 player, electric toothbrush etc comes to mind).

In modern "smart" devices with battery circuits built-in, I would hope they turn themselves off before this happens, and that maybe "0%" is really 10% remaining capacity. I'm not sure about that though.

Well one circuit is 'smarter' than another... ;) But this is one problem I have with "smart" batteries, protection pcb's and similar: it makes a stored battery discharge faster than necessary. If the difference is negligable, okay then. But I suspect it's often not (protection circuit draw >> battery's own self discharge). Which makes batteries sit empty quicker, and thus longer than if no monitoring circuit were present. To have the best of both worlds, you'd need a quick/easy way to disconnect a monitoring board for when a battery goes in storage. :thinking:

 

[Wrend]

If you know battery capacity ('historical records'), a previous State-of-Charge (for example: empty), and know at what rate you have been charging (= measured), then you can calculate remaining charge, time until empty, time until full, etc...

Good point. I wasn't thinking that these internal charger circuits and/or devices might be measuring and tracking current rates too. I suppose some of the "smarter" ones probably do these days.

 

[theilluminati]

Thank you for your excellent answer, however I am not sure I 100% grasp the last paragraph; maybe because I am not a native speaker:

Again, this is only specifically for Li-Ion and Li-Po type cells. These kinds of cells aren't helped much (if at all) in the same way that more fully cycling NiCd and NiMH cells can help them maintain higher performance over their cycle life expectancy (as well as not being left slow roasting on a trickle charger after they're fully charged, as was and is unfortunately sometimes common practice).

 

[theilluminati]

Articles to ponder:

http://www.filterjoe.com/2012/08/08/keep-iphone-plugged-in-yes/

http://arstechnica.com/gadgets/2011/02/ask-ars-what-is-the-best-way-to-use-an-li-ion-battery/

 

[MidnightDistortions]

I pretty much killed my smart phone battery due to me thinking all batteries were the same and always discharged the battery fully. But then something went wrong with the battery anyway (it looked like it expanded) and ended up cracking the screen. Surprisingly it still works but the capacity is greatly reduced which then i decided to get a usb charger so i could charge the phone on the go. I got a new phone that i generally leave off. It was on sale so it was a good buy and eventually when i am better financially situated i'll switch over to the new phone (unless the old one stops working). Anyways after dealing with Li-ons i think it's better to keep them charged to 80% like the article says provided you have a way to recharge them.

Laptop batteries though are a pain because the laptop itself generates heat which the batteries are subjected to no matter what. And those batteries are not cheap to replace either. It's better leave the batteries in a charged state and taking them out when not being used to extend their life. Though it's basically a built in UPS and you could either save your data or go into hibernation when the power goes out.

 

[mvyrmnd]

I have an iPhone. It gets fully discharged by every lunchtime.