QUOTE (DAZZZLA @ Jul 14 2008, 05:24 AM)

It's a temp sensor for charging.
DJ
Yup temp. my DeWalt has the same thing. When you use the drill alot, the batt gets hot, and if you were to do a quick charge while hot, it runs the risk of bursting, or damaging the battery. So the third tab is so your charger "knows" the temp of the batt it's trying to charge, and knows if it is allowed to charge the batt, or if it's too hot to be charged.