2007 Prius: Red Triangle + ABS + Engine Check lights :(

I would leave it on for another 8 hours since it is only a 2 amp charger. After you remove the charger, let the car sit for a few hours, then check the voltage the same way you did before. You can then clear the trouble codes and let us know if any warning lights come back on.

If you do not drive the car and it sits for 3 or more days at a time, week after week, then it is a good idea to use the charger every 2 or 3 weeks. The charger you bought is a smart charger, so it will not overcharge the battery. You could leave the charger connected to the battery for months without a problem.