I've played around with a variety of portable charging options for taking my Z on trips away from electricity. Solar power is a bit feeble and unreliable, and AA batteries are rather heavy and don't seem to really give a very long-life (I've used 4 NiMH cells).
Recently I bought a miniature hand-cranked dynamo, advertised as an emergency mobile phone charger:
It seems to work fine, although I suspect it would take a lot of time to get a full charge. As a top-up, it looks like it will do just fine.