In terms of battery life, the USB power-bank manufacturers aren't making their own cells, and performance will be dependent on the underlying cells and (to some extent) the internal circuitry. I haven't seen power-bank makers advertising where they get their cells from, but Aukey and Anker are well-known makers that you can probably rely on. I've bought cheap power banks that work, but take forever to recharge. There are also some that advertise weatherproofing, which sounds like a good idea, although I don't know if they're weatherproof when your phone is plugged in.

If you're relying on the phone for turn-by-turn navigation, be aware that not all apps offer this, or offer it only for an added fee (like Ride with GPS). I'd always recommend having a printed route-map as a backup.