I find that those small solio chargers are good enough to get my phone running at 40% charge if the battery actually does manage to die (droid). And I've only really had to use it twice so far.

I don't keep the phone on constantly and only use it to check in every so often, and only really leave it on when I'm cruising around a town that has reception. Doing that, one charge can last me at least a couple weeks. You might want to consider getting an extra or an extended battery for your phone as well.