Best way to release the base and get to the locating lugs is to wrap the base of toothbrush in a towel and then use plumbers adjustable grips/pliers to sqeeze gently to deform slightly the handle. That will make prying the base out easier and a similar technique should be used to access and release the locating lugs (see explanation section below)

All good advice and it works too. Ignore Philips advice that the battery is not replaceable. It is, with correct knowledge and understanding. Thanks for posting.