[ltp] Laptop battery storage

[Henrique de Moraes Holschuh]

On Thu, 30 Mar 2006, Mendel Cooper wrote:
> If you're not running your laptop on battery power, it's a good idea to
> remove the battery and store it. That prolongs its life. It's recommende
> that they be stored at about 50% charge (Why? I don't know.)>

http://thinkwiki.org/wiki/Maintenance#Battery_treatment

See the info there, and also check the external links for the in depth
explanations.

> Why? Because those wonderful "smart" LiON batteries only have a limited
> number of charge cycles, something in the range of 200 - 300 or so. And,

Could be a lot more than that, I've seen battery packs rated for 1000 cycles
or more.

Anyway, depending on the manufacturer, the fuse could be a lot smarter than
a cycle counter.  Some will short open if one of the cells get too depleted,
and it will ignore the cycle count, which acts more like an odometer in a
car in that case.

You should look at the cycle counter when you buy a battery, just like you
should look on the SMART power-on-hours and power-on-cycles of a supposedly
new HD.  It might not be as new as you thought...

And don't buy crap, or we won't be able to get ThinkPads in the future :(

> there's an electronic counter inside the battery that keeps count and
> irrevocably turns off the battery when the count is full up. Very clever.

A Li-ION battery is an explosive device, and they require security devices
built-in.  The cycle counter (*if* it is using as a lifetime limit) is not
there to rip you off (but it can be used like that, too).

> Now, when you keep the battery inside the laptop, even running on AC all
> the time, the battery charge trickles down a percent or two a week. And,
> when the charge drops to 95% *, the BIOS senses this and recharges it
> back to 100%. And, guess, what? That counts as one charge cycle. So,

Such usage patterns hose the battery completely, and not because of that
counter.  It causes crystalization inside the Li-ION cells and phisically
*damages* the battery because you kept it at high charge constantly.

IBM's new Windows utilities will try to convince you to keep the battery
around 86%. That on a T43 at least (which has full battery control).

I have mine set-up (thanks to tp_smapi) to stay in the 20%-75% range, and
only charge it fully (or deplete it below 5%) when I need to, plus every
three/four months to keep the battery on its toes.

Spare batteries go to the refrigerator at ~40% charge, suitably protected
against moisture.  Beware of the Li-polymer batteries, they might lose
charge fast (I don't know why, but I've seen it happen once), and you don't
want them to go below 2% on cold storage, so check them monthly at least.

> in about a year and a half you can use up a brand spanking new battery
> without ever actually using it. Very clever indeed.

After one year of keeping a battery at 100% charge at ~25C you will have
pretty much hosed it, it will probably have a "real battery age" of 2.5
years or worse.  I've seen Toshiba batteries treated like that go from 2.5h
to ~10min uptime capacity in one year.

>    * In some older laptops, the recharging would start at 98%.
> 
> Sometimes, those "smart" gadgets are too damn smart for their own good.

Manufacturers still get away selling laptops that keep their batteries at
100% all the time (hello Dell!) and people praise them with more market
share.

Your problem is that a lot of manufacturers (probably even IBM in some
models) don't sell smart *enough* batteries.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh