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.
The view of the top of the 3V battery showing the little fibre plug. The larger pin is clearly marked with a + in the fibre plate. The clock leads are normally soldered into the brass pins but were removed to allow new leads to be connected more easily to another power supply. (The old battery shown here is flat and the original clock leads were badly perished)
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.