Braun electronic toothbrush

Question

I have 3 Braun electronic tyoothbrushes that do not work. They will no longer recharge no matter how long they sit in the charger base/stand. I have thoroughly cleaned them, tried rotating each of them in the different chargers etc. I don' t see any way to open the base of the handle to see what's wrong and I don't know if there's a battery in there that needs changing. I can't find anyone who knows how to fix them. I bought another new one but am worried this one will have the same problem. They are expensive and I would like to know what I'm doing wrong or are these things just designed to self distruct? Help!