My film camera uses an older style battery that is difficult to find, the form factor is ok, but the voltages are different in modern batteries. This affects the meter readings on the camera light meter.
One option is to install a diode in series with the battery, using something like this diode
The fix is relatively straight forward, you remove the bottom of the camera housing
Remove the battery spring clip and desolder it from the wire, place the diode in series between the two and reassemble
The above images are from this link (thanks Tim Hughes)
I'll put togetehr a better pages when I get around to actually doing this, in the meantime, I'm just adjusting for the high metering by guess/gutfeel.