The Mempac range is used in many memory back up applications, particulary for Fruit Machine Backups and  Central Heating Timers, like the Potterton. Many original batteries may of been in a Blue Case, it was Nicad and known as 3V100R. Others with a Honeywell Timer will note that their outer case was Beige and has a small locating peg. This Ni-MH battery is a uprated version of these older batteries.