For cameras using one 1.35V battery (Minolta SRT 101, Nikkormat FTn), use ECG109, Germanium Diode between the battery box to the wire going to the meter board; This will drop the voltage of 1.5 volt alkaline battery.
For camera using two 1/35v battery, use 1N4007 silicone diode in series from the battery box to the wire going to the circuit board.
Put warning labels at the bottom cover for the conversion just in case user wants to use a zinc air battery which is 1.35v and no conversion is needed.