Battery Life Update

June 13, 2009
Posted by: Butterman


Remember this flashy hunk of lithium? MWeston has been testing it in the new prototype Pandora and has got some numbers for us! *Cue MWeston*

I have an EVM for the battery fuel gauge so I can connect that to my laptop and log the battery draining from start to finish through the USB port so it doesn’t matter if the Pandora board shuts down on its own when the battery is empty. I still haven’t done a full charge to empty cycle all at once but the fuel gauge learns the battery profile and was predicting the usual 8.5-9 hours. Since I have run the battery down over a couple of days with my testing, the prediction is accurate as the battery capacity is at or above the rating given by the manufacturer.

The load doesn’t change much whether you idle at the desktop or run an emulator or app. I think the change is around a 50mA range based on processing and how quickly the pixels are changing so doing pretty much anything with just the CPU core is going to perform about the same. Average power with the LCD at full brightness is around 1.6W. Adding the SGX core into the mix (like with Quake) added another 30-60mA of drain I think. It fluctuates with what’s going on. It’s been a couple of months since I have run these tests but the hardware hasn’t changed to affect new results with production boards so this is all still valid.

What really changes the power usage is when the LCD goes off, cranking up the internal speaker volume or plugging something into the USB port (a simple mouse or keyboard will decrease battery life by 22-25%. That’s how little the whole system uses!). If you slow the clock for things that don’t need it (I run Picodrive at 200MHz in Angstrom for example), you get the 10 hour life and if I turned down the LCD brightness it would be a bit more.

When the LCD goes off and I’m playing music, the battery life was in the 12 to 15 (if I remember to slow down clock) hour range. We still don’t have power management in the code so everything is lit up, the core is running at the voltage for 500MHz and the clock was usually at 500MHz so there is all kinds of room for improvement. If an N900 or Palm Pre can run all day on an 1100-1500mAh battery (maybe?), we should be able to do way better with 4000mAh. The hardware has the capability to shut down anything not in use so it’s purely a software effort needed. We only have one person volunteering to work on the power management code right now so software seems to develop at a slow serial rate with the extra stuff like this.

EDIT: I also don’t recommend going around boasting a 100 hour battery life playing music. As some people have pointed out, getting anywhere near that will require some serious talent to code. That might be a community project some day but no one should count on that as a launch feature to shame your iPod buddies.




  1. This is great to know, very informative. I haven’t seen it specified, but how easy are the batteries to remove, what are the charge times, and will spare batteries be available?

  2. i like the last part. about being realistic and not claiming 100h battery life while playing music. However, TI released code to the gstreamer project which uses teh DSP…

    I would like to have a detailed listing what part uses how much power. I always wondered how much a headphone or the speakers or the LCD use up. With this nifty tool of yours it should be possible to make such a list ๐Ÿ™‚

  3. ๐Ÿ˜€

  4. oops, my last post got screwed up. @ GM dude, the battery is easily replaceable. you just pop the back cover off and take it out, simple as that. replacement batteries are also available. also, don’t quote me on this but, i think the charge time is 4-5 hours.

  5. Well, I hope that we can at least reach 20 with just mp3.

  6. i still think there’s a chocolate bar in there.

  7. guys, post a resized picture! there’s no reason to have a picture that’s like 1800 pixels wide if it’s just gonna be resized to 600.

  8. Quote from Kramy on the forum tread:

    “The CPU uses about 0.05w, and the LCD about 1.6w. Downclocking will knock that down to 0.04w, which doesn’t save a whole heck of a lot of battery life.

    The Pandora as a whole should consume around 2 watts. If the LCD needs 1.6w, then you can shave off a max of 0.4 watts by downclocking and shutting stuff off. More likely, 0.1-0.2 watts. (5-10%) The biggest power savings will obviously come when the LCD can be turned off.”

    So it’s really not realistic to expect much more than those 8, 9 or 10 hours of use, without turning off the LCD.

  9. It’s great to know that we really in fact can expect up to 10 hours of real use though! ๐Ÿ˜€

  10. Plus who needs that backlight when your listening to music. Considering the backlight is about 80% of our power draw turning that off should give us around 18 hours of battery life. Plus if we could underclock some stuff and turn various unneeded hardware off that should be another 100-200 mW, which would give us about 1 more hour. With proper optimization I think we could see 20+ hour mp3 playback. I wonder if we’ll also see some high capacity (as if they weren’t pretty high capacity as it was ) battery’s latter on in Pandoras life as well.

    Overall I’m really satisfied with the Pandoras battery life considering I’ve been accustom to my PSP wimpy 3 hour AT BEST battery life >.>

  11. So if the Pandora as a whole consumes about 2 watts, and the LCD is responsible for 1.6 of them (i.e. 4/5 of the total power requirements), and the battery can service the 2 watt requirement for at least 8 hours, then shouldn’t we be able to get 5 * 8 == 40 hours of LCD-less processing out of the machine?

    Unless it takes almost as much to power a headphone jack as it does to power the LCD(??), I’m quite confused as to why the estimates for playing mp3s are so close to the estimates for playing games with the LCD on.

    Is this is just a part of the software issues referred to, or will the LCD really draw lots of power even when it’s not required?

  12. On the upside, overclocking will give a pretty significant performance increase with little loss of battery life

  13. Nevermind my math was off. I reworked it all out and your right. We should be getting 40hours with the LCD backlight off! Thats much better peculiur because MWeston says he had this same exact setup and got only 12 – 15 hours of battery life… there is something seriously wrong there…

  14. Hopefully it’s not hard to write some power management code that will shut the screen off when you’re simply playing mp3’s. If anything, I should hope for at least an icon or something that could do it manually.

  15. We’re told the magnetic sensor in the lid is going to be user configurable (in software), so you can have it do whatever you like when the lid closes. I’d like mine to trigger a .wav saying “Father nooooooo!”

  16. Oh you do crack me up Gruso ๐Ÿ™‚

  17. As far as I remember You can also remove the battery and run the Pandora just via the power adaptor?

  18. Guys, The quote that says the LCD consumes 1.6 Watt is wrong.
    The whole system consumed 1.6 Watt on average.

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