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I have a 3.7V 4.4Ah li-ion battery and would like to use it to power my Raspberry Pi (which needs 5V and 700+ mA). What’s the easiest way to do it with minimum EE experience? Also, what resulting running time can I expect?

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The easiest way without having to do any EE experience would be to buy a boost converter module. You might probably get a little under 4.3 hours.

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Once you've found a suitable boost converter a simple way to think about power consumption is to think in terms of watts used per hour. So 5 volts at 0.7A which the Raspberry Pi requires is 3.5W (just multiply together). For your battery 4.4Ah x 3.7V = 16.2 Wh, so 16.2 / 3.5 = around 4.6 hours of operation.

Then you'll have some loss in the converter, 80% efficiency is probably a good conservative value to use so 0.8 x 4.6 = 3.7 hours of operation. It won't be exact but will give you a good simple ballpark figure.

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Divide the Ah for the battery by the load current, to get the approx. running time. It'll actually be less than that, because the Pi will stop running before the battery is discharged, when the voltage drops below the minimum.

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  • \$\begingroup\$ Thanks! I have figured out the 4,4Ah/0,7Ah formula, but have no idea how much the boost module changes the outcome. \$\endgroup\$ – zoul Mar 23 '13 at 9:07

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