If you are interested in buying some rolleiflex cameras or accessories,
The batteries are described in the SRT owners manual in this way.
“The Minolta SR-T 101 uses a 1.35v, button-shape mercury battery for photo-graphic applications (Mallory PX-625, PX-13, Eveready EXP-625, EPX-13 or equivalent). “
These mercury batteries your SRT was designed to use are now very hard to locate, as production has been discontinued in most of the world for very good environmental reasons. There are a number of possible replacements, but none of them result in exactly the same meter readings as the original design, at least without some effort at recalibration. This is because the meter is a very simple circuit which depends upon a specific stable voltage source.
There is a tremendous amount of data on the web regarding ideas for replacement power sources. I think most of these solutions are viable for the SRT application, assuming you have the capability to recalibrate your camera’s mechanical and electrical systems. Ok, I’ll repeat it, I don’t think there is a really ideal solution, without doing some recalibration. It might not matter too much, because it is entirely possible that that 25 year old camera of yours needs recalibration, even if you still use mercury batteries. In any case, once you get the hang of it, and build yourself a tester, recalibration is not very hard to do.
Here is a table detailing some of the possible mercury battery replacement options. This is ordered with my preference at the top and least desirable solution at the bottom. I highly recommend that whatever solution you choose, that you consider calibrating your meter for maximum performance with that power source. See my meter tune-up page for more information.
via srt-mercury battery.