Those alkaline batteries in the PX625 form factor aren't a proper equivalent because they put out a higher voltage (1.5V). The alkaline batteries also gradually drop voltage as they deplete, while mercury (and Silver Oxide) tend to hold their voltage until they're nearly done, and then drop fast (Silver Oxide cells are usually 1.55V). Unless the camera has a voltage regulator of some sort, the modern replacements will result in shonky meter readings. I've tried them in an Olympus 35RC and a Rollei 35S, and both were off - and not linearly. I seem to remember tweaking something in the 35RC to get it to match a reference meter, but found that it was out at different brightness levels. (The Rolleis have two trim pots inside - one for the basic reading, and one to adjust the linearity of the readings over a range of brightnesses. I've still to calibrate my Rollei to use Silver Oxide cells.)
The only drop-in option if the camera has no voltage regulator is a wien cell, which has a short lifespan. A seal is pulled off to open a vent, at which point the battery puts out a voltage very close to the mercury types, but they only last a few months.
The only drop-in option if the camera has no voltage regulator is a wien cell, which has a short lifespan. A seal is pulled off to open a vent, at which point the battery puts out a voltage very close to the mercury types, but they only last a few months.