A number of non-striking clocks in my modest collection had a space cut out in the case for a much larger than normal battery. All Telavox striking clocks seem to require a standard 4.5Volts flat style of battery whether they strike on a bell or gongs.
Finally I have found a clock with an original large battery still in place! It turned out to be a very large, two-cell, 3 Volt battery with a socket in the top for a two-pin fibre plug. An image appears below showing the large battery beside two of the normal 4.5Volt batteries.
A collection of 4.5V batteries. Many of which are now flat and need to be disposed of. The larger 3V battery used in non-striking Telavox clocks is on the left.