I've just bought the product, so it's impossible to answer the question of how long it will last. On the other hand, the battery seems to be very efficient when it comes to charging; it lasts for 5-6 days without any problems, or even longer...

If you brush your teeth for about 2 x 2 minutes a day, it will last a good week.

5-7 days

over a week

Easily a week e.g. through the sports holidays without charging.

It's hard to tell, but it's still on its charger cradle.

Couple of days