Is an external batter charger powered by AA batteries a viable option? Most of the external chargers I have seen are rechargeable units. Just thinking a long distance ride, with short stops and questionable availability of electrical outlet charging options, would make this type of charger a good option. I've never used such and don't know if they provide sufficient charge to be worth it. Or would they be better as a "backup to the backup"? ***Edit-- Looking at this option just due to convenience and possible lower weight penalty. This would be in a long distance, randonneuring situation, where were have a limited time to cover 400, 600, 1000 or 1200 kms.***