Powermonkey Battery Capacity

Testing the reassembled Powermonkey under various loads proves instructive:


The relatively low capacity at 100 mA (black) shows that the boost converter isn’t particularly efficient; the discharge time is long enough that power loss in the booster outweighs the cell’s higher capacity at lower loads.

Surprisingly, the voltage drops to 4.5 V at 500 mA, which is what you should get from a typical USB port. If the device you’re charging expects the nominal 5 V at 500 mA, it will be sorely disappointed. Admittedly, that’s only 10% low, but …

The booster produces only 4.0 V at 1 A, with odd bumps as the cell discharges. Huh?

I know for a fact that my 1.8 A @ 5.0 V Kindle Fire doesn’t even notice it’s plugged into the Powermonkey. The voltage is probably too low to trigger the “External Power, Ahoy!” signal.

Bottom line: it’s not clear this thing actually works for contemporary devices. Maybe newer Powermonkey products behave better?

3 thoughts on “Powermonkey Battery Capacity

  1. hack dat mcu and give it more BOOST less BUCK

    speaking of bucks, hopefully it was dirty cheapness…

    1. smaller resistor on an input

      I could fiddle with it, but it’d require dismantling the PCB and scraping off all the foam tape goo… and I doubt it’s worth that much effort. [mutter / grumble]

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