Does the battery have to be fully charged before it can be powered off?

Answer:

Generally, when the second frame of the charging progress bar starts flashing, you can disconnect the charger and start your vehicle.

If you are in a hurry, you can disconnect the power at any time. Disconnecting the power midway will not have any adverse effects on the charger or the battery.

Note: Click on this link for details on the charging time of batteries with different capacities: How long does it take to fully charge my battery with Sigma 1 battery charger?