The side bar on those batteries is that they contain three 1.5V cells in series. And each individual cell is the correct size for the battery in the oldest of the AVO multiminors.
So you buy one, split open the outer case and you get three batteries for Multiminors.
£3.62 from RS
https://uk.rs-online.com/web/p/speci...eries/7904697/
https://docs-emea.rsonline.com/webdo...6b81583229.pdf
Craig