The battery of this toothbrush does not last very long, for me it is about 10 days. 5 days is definitely too little - have the part replaced via Philipps customer service. They don't do a bad job at all.

Brushing 2x a day, 3 - 5min each (I also forget the time), 12 days holiday - top product. My dentist recommends the product unconditionally (at least for my teeth and gums) :-))

Of course, it depends on how often and how long you use it. I often forget the time when I brush my teeth :) and so it runs for about 7-10 minutes a day. So it lasts for almost a week, which is easily enough, or why do you find that disappointing?