Ok, I did my little experiment with a power supply. Not that this helps M-3PO, but some of you might find this interesting.
It’s probably best to add a bit of a dislaimer here. I advise everyone NOT to do this. If you hook it up wrong, you will very likely blow your clip out. If you set the voltage wrong, you will likely blow your clip out. You might even gets some nasty smoke. I’ve been designing hardware and software professionally for over 30 years and (I think) I know what I am doing. So don’t even think about blaming me if you do something bad to your clip.
I cut a USB-A to USB-mini-B, tossed the USB-A end into a junk box and trimmed back the ends on the red and black leads on the mini-B half. I hooked the Vbus and ground to a high quality bench power supply set to 5.0V (not a cheapy wall wart). D- and D+ were left unconnected.
I plugged it into my clip (which was off) and it came on, drawing around 140mA. The battery charge animated icon indicated it was charging and I could play music, listen to the radio, etc., as it continued to charge.
The current varied from 120-140mA as I played with it. (It is out of the 100mA spec!)
When I turned the clip off, the current dropped to 0, therefore it is not charging when off.
So, a 5V/150mA charger should do the trick. 200mA to be on the safe side.
I think I’ll hook it up to a 4xAA, 2.6Ah NiMH battery pack (4.8V) and see what happens. That should run it good long while. (Note here that if you try this with 4 Alkaline batteries, it’ll probably blow your clip out because 4 of them would be 6V, Alkalines are 1.5V, NiMH and NiCd are 1.2V)