Everything I Knew (About Battery Care) Was Wrong

[ellenkushner]

I just copied this from the website Cogito, Ergo Sumana by Sumana Harihareswara; it was sent me as a link on Twitter by the kindly & helpful BrendanAtkins when I Tweeted about trying to run my iPhone batteries down. It will alleviate many domestic disputes, as deliasherman has just gotten a fancy new MacBookPro for which my soul panteth as the hart after water, esp. given that my own MacBookPro 3,1, purchased not all that long ago, is now down to 38 minutes of plug-free battery power (FEH!!! and yes, I have tried running it all the way down & letting it charge w/out hindrance. Things do not get better but worse), while Delia was told at the Apple Store to let her MacBook run down ALL THE WAY EVERY TIME SHE USES IT to keep the battery tip top, and let me tell you it is very annoying. She's now after to me run down my iPhone, but - AHA! Read on:


Everything I Knew (About Battery Care) Was Wrong: Today I learned that I've been working from an obsolete understanding of how to keep my cellphone and laptop batteries from losing gobs of capacity over time. A simplistic summary follows for your benefit.

The batteries in my phone and my work laptop are lithium-ion batteries. Check yours -- the "Li-Ion" abbreviation means it's lithium-ion. As detailed sources explain, charging/discharging battery care for lithium ion batteries is the opposite of the conventional wisdom I had in my head, left over from the old days of nickel-based rechargeable batteries.

It used to be that you'd want to run batteries all the way down before starting to charge them again, because otherwise the capacity might get messed up. That's not true with lithium-ion batteries; it's recommended that you only rarely let an Li-Ion battery run down below 10% of its charge.

Lithium-ion batteries lose capacity, in the long run, if they sit overcharging a lot, or if they run hot a lot. So don't let them sit plugged into a charger all the time, and if you usually run your laptop plugged into AC power, think about removing the battery and setting it someplace cooler. [I'm not sure what she means by that - ek]

The moment a lithium-ion battery gets manufactured, it slowly starts losing capacity. So buying a primary battery + a spare battery simultaneously might be a worse decision than using a primary battery, then getting the spare battery years later, when your capacity has substantially degraded.

This came up because I assumed I should let my new N900 run down completely (on the partial battery charge from the factory) before plugging it in, and I was annoyed that plugging in the USB-to-microUSB cable to transfer files meant it was getting juice while the battery hadn't totally discharged. But I was wrong to worry! Thanks for straightening me out, Sjoerd.

Comments

[shweta-narayan.livejournal.com]

*head explodes at the small-world in which you're quoting Sumana.*

[I'm not sure what he means by that - ek]

Sumana's a she, btw :)
And I think she means it literally -- if your laptop or cell phone is normally plugged in, and the battery gets hot a lot, you should maybe take the battery out until you need it? The only problem being that if you forget and unplug the device, it goes kersplat.

elsmi has our laptops set up to only charge to 60%, and stay that way, unless we explicitly tell them to charge all the way; we can therefore leave them plugged in without screwing up the battery. I have no idea how this bit of computer magic is accomplished, though, and whether it's possible at all on a Mac.

[bluestalking.livejournal.com]

...All I can think of when I read this is my psychiatrist shaking her fist and shouting, on behalf of psychia-kind, "STOP WASTING OUR LITHIUM! STOP JACKING UP PRICES ON THE ONLY CHEAP DRUG WE HAVE THAT WORKS!"

She has strong opinions, and they make me very happy.

[prosewitch.livejournal.com]

Hey, neat, Sumana and I went to Berkeley together!

[eclecticmagpie.livejournal.com]

I was getting MISERABLE battery life on my MBP, in particular when it was asleep and I was traveling, and recently found out that the top cover switch that tells it to go to sleep AND STAY ASLEEP was faulty, so it was turning on in my bag and running down the battery. Turned out there was a software solution; now I have to press a key to wake it up, instead of just opening it, but I get decent battery life while sleeping. I'm told it's a common problem for some models.

[jennygriffee.livejournal.com]

I'd think about taking the battery out if it weren't so. freaking. easy to unplug the computer with a touch, at which point the whole thing would just shut down on me without warning.....

MagSafe: blessing or a curse? ;)

[erink.livejournal.com]

So, wait, should we run it down or let it charge? I'm so confused.... (Aren't most batteries lithium-based now?)

At least I'm not the only one - a few years ago I bought a Scooba robot to clean my kitchen floor, and the battery would always die before it finished. The manual said to leave it plugged in (theoretically, charging) all the time - which I'd always thought was bad. Eventually I looked up troubleshooting info on their website, and their advice there was to charge it only when you were going to use it! (I did get a new battery under warranty, but I've just replaced that one too.)

[deliasherman.livejournal.com]

I'm with Erink--very, very, very confused.

Which is pretty much my normal state of mind, vis a vis technology.

Down to 6%. I guess I should plug in now. And unplug when it gets charged and then plug again when it's at 30%??????

All I want is a simple rule.

Original link, & wave

[brainwane (from livejournal.com)]

Hi! In case you want to see my original post, which has some links to source texts (some people know A LOT about how batteries work), here you go:

http://www.harihareswara.net/sumana/2009/12/19/0

Hi Shweta! Hi Jeana! And hi again Ellen! The battery info is the least I could do for you after you found me those awesome clothes at the WisCon clothing swap, and read that lovely story on New Year's Day.

[elswhere1.livejournal.com]

Wow; I had no idea. Thanks!

[(Anonymous)]

When I bought my MacBook two years ago, I was advised to let the battery run all the way down about once a month and let it wait about fifteen minutes before recharging. Seems to work, since it still has 5 hours battery time...

best, Johanna Vainikainen-Uusitalo

[lianneb.livejournal.com]

I seem to recall reading that yeah, don't drain it every time, but once in a while you do need to drain it, just to make sure that everything is still registering properly. This includes even things like MP3 players.