Icom IC-7100 RTC Lithium Battery replacement

Icom IC-7100 RTC (Real Time Clock) Lithium rechargeable Battery replacement,
Fault, IC-7100 not keeping date and Time.
The battery is located in the Main control unit.
The battery i Have used is NOT a direct replacement.

Original Icom Part number BT6201: ML414HIV01E
Replaced with MS621FE, 3V rechargeable Lithium Li-ion battery.

Not one of the easiest Batteries to replace, I would recommend using a Hot air gun with protective Kapton Tape covering the surrounding components.
I would recommend placing  a piece of insulating tape under and over the battery.
NOTE: do at your own risk, this is just a guide  to the location of the internal battery.