pink leakage from rechargeable toothbrush?

my boyfriend has an oral b braun rechargeable toothbrush that keeps leaving a hot pink ring on the sink, after looking at it the pink substance is in the head of the toothbrush as well. so i just attributed it to this drink powder he uses before going to the gym… well he hasn’t used the mix in about a week and there’s still hot pink stuff on my sink and on the toothbrush…. anyone know what it is?????? is the battery leaking?????