3rd party chargers?

[Tsurugaya]

USB won't work.
USB is only 5v
SP3 needs 12v
You need a battery pack that can output 12v, and it won't be able to do that via a USB port.

I have the Intocircuit 26000 which I used a lot for my SP1, but haven't bought an SP3 cable yet as they were about $100 last time I looked.

That Nuosi Deng one for $19 looks like it might do the trick though.

Excellent point, out of curiosity, wouldn't a 5V charge be enough to trickle charge, in other words it just takes a much longer time?