I have an Edge 800, about a year old, OS maps which I personally love (but I haven't tried OSM or anything else).
Any old USB A to Mini plug should sync fine, unless it's specifically "charge-only": I use whatever's lying around. I DON'T use the one I use for charging on the bike, because I would forget to place it back in my Carradice and would end up charge-free after about 8 hours. I would just get one of the Lindy or StarTech cables from Amazon, as they are reliable and inexpensive.
I've used battery packs and long USB cables and I am currently using USB-charging from a dyno-light, which is so obvious and straightforward that I much prefer it; I have a short cable with an up-angled USB-Mini connector for this (the USB socket is upside down on the 800, so the cable drops downwards, which works for me). Avoid charging in the rain, though, as damp connectors will prevent all charging until it's completely dry, which might be next week some time.
I get about 8-10 hours battery life normally with it set to a data page showing speed, cadence, heart-rate, distance, clock, compass and not much else, plus I usually have a route loaded with turn-by-turn directions as well as custom cue points to keep me awake. I wouldn't be surprised that having ANT+ sensors connected drains the battery too, and I have two of those.
Because I can charge from the dynamo ad infinitum then at night I like to keep the brightness low and the backlight on, otherwise I find my pace drops inadvertently.