OK, here is a well "Duh" moment on Mark56.... even my Boston Scientific internal unit warms when charging if I have allowed the residual power of the internal unit to de-charge too much before a recharge session. Especially my external charger will become warm to the touch if charging for longer than 45 minutes during a session.

Having learned thus, I attempt to charge my unit for 30 minutes at a time.

Yup,
Mark56