The Crompton Parkinson DS7 was a 1 ½ V dry cell that was available in the 80s. This one has a date of 5th June 1984. The box is approximately 3 cm × 3 cm × 7 cm in size. It also has the following numbers on it.
Many Avometers have a square recess in the battery compartment for a 1.5 V battery, and it appears it was specifically for this type of battery.
Opening the box, there is a metal cylinder with a brass positive terminal. The sealing at the top appears to be a tar-like substance.