If your Sonicare feels like it lost it's power it could be because of a misalignment of the magnetic motor, e.g. after a fall. Philips built it like this on purpose and you need open the toothbrush and realign the magnetic motor.
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'''Caution:''' Please only proceed if your toothbrush is out of warranty. If you still have warranty:bring it back and get it fixed by Philips.
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Follow this guide to fix Philips Sonicare DiamondClean HX9340 after loss of power or weak brush.