A short length of electrical tape and you're good to go!!
A short piece of electrical tape resolves the water infiltration issue where the battery base connects with the brush holder.  My experience with the rechargeable units was that they lasted for 2-6 months and then died.  Phillips was pretty good with warranty service but the no charge replacement handles again lasted around 2 months.  For the AA battery model I recommend fresh alkaline batteries rather than reusable/rechargeable AA's.  The battery contacts in the brush handle sometimes dent the battery electrodes and can interrupt the connection.  Fresh AA's quickly resolve that issue.  I probably get 2 months from a set of AA batteries.  The brushing action is exceptional and this Sonicare provides strong performance and great value.  Seal the battery compartment from water with electrical tape whenever you load fresh batteries.
Rating: 4 stars