Hi ya,
I got an old TMK multimeter. The 15v battery for the highest
resistance range needs replacing. It is a number 504. Any
suggestions please on a cheap and compact way to substitute this
battery? Thanks,
Dave

If this is the same battery that is used in the Triplett 310, it's still
available from test equipment dealers.

The Triplett 310 is a living dinosaur, I mean classic.