Spare battery: remove empty battery, switch battery, you are back to 100%
Powerbank: mess with cables, keep phone plugged until it's charged and wait
If there is a market for spare batteries, there might be a market for external battery chargers as well > swap battery in the morning instead of charging, place empty battery on charger, repeat the next day
If there is a market for spare batteries, there might be a market for external battery chargers as well > swap battery in the morning instead of charging, place empty battery on charger, repeat the next day