The waterproof requirement is a deal breaker for me, I live in Oregon. Plus I'm sure I'd get the usb connection full of dirt etc. If you are a fair weather rider, what your suggesting might work. The battery life is great as you point out, so that's likely sufficient for most. I wanted something that 'just worked', regardless of weather, how long I was on the bike etc. On my day ride or less bikes I don't hardwire it, I rely on the battery. I should carry a USB charger too, in case I'm stuck somewhere for a LONG time or forget to charge etc. Not that I've found, but if someone does find one I'd love to hear about it.