When you plug a nuvi into a computer the assumption is that you want to transfer data to/from it so no charging information is shown. That said it does charge (I've done it on occasion).
BTW you can use any USB power adapter (from AC power or car cigarette lighter) to charge nuvi's. That said some (and you can't tell just by looking at them) will cause the nuvi to think that's it's plugged into a computer.
What I do is to use a (genuine) Garmin power cable for my nuvi with a AC power-cigarette lighter adapter. Works great.
As Stuart says there is no indication of battery charge. I generally (should I need to charge it at home) leave it for a couple of hours, that seems to fully charge it and will do no harm.
