Looks like Power Monkey, oo-oo-oo.
I have used the excellent little Power Monkey portable charger for a few years for travel for phones etc... (holds it's charge for yonks) - I tried it today and it put a charge into my 350 - I'll try again tonight, but all are pretty well charged up.
Will report, but it looks OK.
If I'm right, Power Monkey's the answer.
Surprised I haven't tried it before.... grey cells are going....