Unfortunately, I can't tell you exactly, but I would rather assume 336 hours, which corresponds to a time of 14 days. But that's not 336 hours of brushing, it's 14 days of normal use without having to recharge the toothbrush! I can also say from experience that this is true.

The 336 hours would be 20'160 minutes of brushing ;-)
If we assume that you really brush your teeth a lot and for a long time (which may well be the case, because it really is more fun to brush with this brush) and you therefore brush your teeth for 3x4minutes=12minutes a day, the battery would then last for an incredible 1680 days. So you wouldn't have to charge the toothbrush for 4.5 years.... muahaha... sorry