Raspberry PI - battery ?

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Has anybody found a good battery solution for the Pi that will let it run without regular wall power for a decent length of time - 2 or more hours?
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Principal Software Engineer
Commented:
The various models of Raspberry Pi run from +5 volts DC.  Consulting the specifications, the maximum current draw is 2 amps.  This loading (2000 mA) is at the outer edge of what can be expected from a "small" battery pack.

A high-capacity portable USB supply (typically used for charging phones when no AC is available) should do the job off-the-shelf.  Derate the manufacturer's claimed capacity by 50 percent as most "power packs" are rated generously by the manufacturer; therefore, figure on the basis of a 4000 mA load, not 2000 mA.

Given that loading, a 10000 mAh (milliAmpere-hour) pack should run a Pi for 2.5 hours or more.

Newegg 10000 mAh USB packs

If longer runtime is desired, a motorcycle battery with a DC to DC converter would be the way to go.  It would be a heavy and clunky solution, but that is the way batteries are.  More current requires more mass.
Most of those USB packs just have three or four 3.7 Volt 18650 Lithium cells and a voltage / current regulator and a built in charger.  If you want it light weight, you can just get the batteries and use a 5V voltage regulator chip to maintain the correct voltage and a 2 amp current regulator chip to limit the maximum current flow.  You can then use a separate charger to charge and use more batteries.  That would be much lighter than a lead acid motorcycle battery and DC to DC converter.

12V-5V DC-DC converter  The input voltage can vary between 8 and 23 volts.
http://www.amazon.com/Nextrox%C2%AE-Display-Supply-Converter-Module/dp/B00CBCGAL8/ref=pd_sim_e_4?ie=UTF8&refRID=0F1V8A48TTVR458QDNH4

18650 Charger
http://www.amazon.com/NITECORE-Intellicharge-universal-EdisonBright-converters/dp/B00GODG3X0/ref=pd_sbs_sg_2?ie=UTF8&refRID=1Q934GCC0GE9PZ5224NZ

18650 batteries
http://www.amazon.com/4pcs-Panasonic-NCR18650B-18650-Battery/dp/B00C26OWGS/ref=pd_sim_p_1?ie=UTF8&refRID=0MGAQFN2NM8RT0HPAWZD

You could possibly take apart the USB packs and add more 18650 cells in parallel to increase the total Watt hours, depending on whether the existing circuit can handle it.
Danny ChildIT Manager
Commented:
You also may want to look at either the B+ which has been out for a month or 2 and uses less power, or even the A+ (ditto) - launched just this week, I think?
http://www.raspberrypi.org/raspberry-pi-model-a-plus-on-sale/

What are you using it for?  good to know for power calcs...
Danny ChildIT Manager

Commented:
hmmm... seem to have lost a comment of mine above.

Think I said that which model Pi are you using?  The recent update B+ is lower power, and so is the brand new A+

Author

Commented:
Thanks to all. I have all the Pi incarnations at this point.
Sean OhlrichIT Manager

Commented:
http://www.uugear.com has a cool module called "Witty Pi" that allows for programmable power-on and power-off of the unit.  By being able to turn the unit on and off by a schedule you could extend the normal battery life dramatically.  Just a thought.
I measured the draw to about 0.31A with WiFi dongle + bluetooth dongle, no monitor or keyboard (that adds 0.05A.  I use a battery pack sold at airports for iPad and iPhone.  It lasts 6 hours.   Note that you can also use a 5v solar panel (search eBay) connected to the battery to get yourself through the night if daytime is bright enough.

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