OLPC battery life: What's the real story?

On Sunday night, 60 Minutes reran a segment on the OLPC (One Laptop Per Child) project originally broadcast in May. I missed it the first time and never got around to watching it online (in Windows video format here, for example; there's a full transcript on olpctalks.com).

Hearing OLPC representative Walter Bender repeat the claim of "10 or 12 hours" of battery life "with heavy use" reminded me of an open question from the last few times I blogged about the OLPC project. What is the battery life of this machine, really?

Back on July 21, the News page for the OLPC wiki (archived here) said this:

We ran battery-life tests on 75 B4 laptops: results will be reported on the OLPC wiki this week.

But I looked around on the wiki during that week and didn't see anything.

So while Andy Rooney was blathering on about kitchen gadgets he doesn't use, I started looking around again, and I finally found results. It was a roundabout search. The OLPC wiki's own search engine can't look for multiword strings, and Googling the site produced no results for "battery testing," but "battery test" gave me a page of test results without any explanation.

That led me to a bug report on the OLPC developer site and an explanation of the results back on the wiki. Whew.

As it turns out, battery life is not very good. The best of the NiMH (nickel-metal hydride) batteries produced a little over 4 hours of operation. Of the two brands of lithium-ion batteries tested, one was about the same as the NiMH batteries; the other ran for a little over 5 hours. (Some of the NiMH batteries died after only a few minutes, but the bug report explains this away as a firmware problem.)

And this was with the machine idling--running nothing at all. Under "heavy use" it's likely the battery life will be less than two-thirds of these figures; maybe half or less.

I am certain that battery life will improve over time as the software and hardware are tuned, but these numbers make it pretty clear that the claim of "10 to 12 hours" is no longer within reach. That's disappointing. To me, this means that much of the long-term promise of the OLPC project can't be achieved until the next major revision of the platform.

I've sent an e-mail to the OLPC project asking for updated information, and I'll pass along whatever I get here on Speeds and Feeds.

[Charbax]

There is a black and white low power mode..

And I think they only recently started optimizing the DCON process that shuts off the main CPU most of the time when it's not needed, saving a lot of battery time.

The black and white mode reflective mode consumes much less power, so the numbers might be in such e-book mode when DCON will be kicking in to put the main CPU on stand-by mode.

[Peter N. Glaskowsky]

Good points

If the CPU is running without benefit of power management-- like PCs often do before OS-based power management kicks in-- then perhaps these test systems are consuming a couple more watts than they ought to. But this also means the OLPC must be a long way from being production ready.

The backlight issue is another good point, since the tests were performed with the backlight on-- but the most common operating mode of the system will be indoors with the backlight to get a color display, so I'd have to count this as "heavy use" in the sense of the original 10-12 hour claim. Reading a book outdoors in sunlight isn't heavy use by any standard (and I doubt anyone's going to spend even 4 hours a day doing that anyhow).

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[Jim Gettys]

Ebook mode lifetime - > 13 hours.

Yes, we are not finished with power management. There are several major power savings yet to be had, when running in typical operation.

The major feature we have is the ability to read books (screen on, but processor suspended). In this mode with the screen on (something unlikely to be the case for any human I've ever seen). I have measured this at over 13 hours, occasionally flipping pages (the system wakes up extremely fast).

[Peter N. Glaskowsky]

Thanks for the info

I also appreciate all the additional data you provided in email, and I'll post a follow-up soon.

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