I just took my MX700 out of it's charger, and my finger happened to stray onto the metal contact in the base. I now have a blister on my finger!
I had noticed that it sometimes wouldn't seat properly in the charger, and heard a very feint clicking sound in time with the flashing green light, which I ignored. My guess is the clicking was arcing at the contacts, which over time was enough to heat up the contact point! OW!