You could fit it with a silver 1.5v cell (I forget the number). May need an O ring spacer to keep it in place. If the extra voltage is a problem then a Schottky diode can be fitted in one of the cell connections to drop the voltage by 0.2v

If you want to do a quick test to see if the 1.5v affects the meter, buy a PX625A cell. This is a 1.5v alkaline cell in a PX625 package.

An alkaline battery has a voltage fall off once it starts running out and is not as stable as a silver cell but a new cell will tell you if you need to re-calibrate or have the diode fitted.