Merc-o-Tronic model 98 ignition analyser

[wristpin]

I have one of these acquired 40 years ago second hand. Even then it was impossible to get the correct Burgess 4F5H 7.5 volt battery in the UK and I modified the case to accommodate a battery of approximately the correct voltage that was physically bigger and available over here . Then that battery became unavailable and it's been sitting unused ever since!.
I do a lot of work on vintage engines with points, coils and condensers etc and it would be quite nice to have it up and running as well as my German Prufex set that requires a 230v mains supply. When car batteries had exposed cell terminals it was easy to take an 8v tapping but now, no exposed terminals.
Any suggestions?

Batteries of the day. Ever Ready 715, Olin 5605,Ray-o-vac 903, Mallory 903, Duracel PC903, Neda 903, RCA VS139

[bgsengine]

maybe consider engineering yourself a transformer for a 9V battery (or a 12v automotive battery?) to step it down to 7.5V ? just a thought... just a matter of getting the winding count right I would imagine.. or maybe just buy one .. https://www.ebay.com/itm/9V-12V-15V-24V ... 2451433844

[RoyM]

I remember those well, had a shot that parked me on the floor.

[madmantrapper]

Use a voltage divider, never seen a transformer work on DC.

[StarTech]

Wirstpin,

If you say you have the room for the Rayovac 903 then it is still available here in the US; although, for a little more you could go with the 803 Alkaline instead of the zinc/carbon a long life and smaller too. As operating off batteries it depend on you amperage emand you use 5 D Cell Nicad 5Ah in series to give you 7.2 vdc if you operating short term and just recharge as needed.