Mine has a Varta 625U in it, and it seems to work fine. It looks like a slightly larger than usual watch battery. The original manual recommends a 1.35v mercury battery, but those are no longer being manufactured as far as I know.
"While you're out there smashing the state, don't forget to keep a smile on your lips and a song in your heart!"
Great camera. I had a 7 that I bought new in 73 or 74. The electronics finally rotted out and I had to can it, but I did so with great regret. I now have a T4 that serves the same purpose, but I still miss the 7.
I used alkaline and silver batteries in it with little trouble over the years and very little noticeable difference in meter accuracy. One exception: lithium. It killed lithium batteries in very short order...don't know why, but I'm sure somebody here does.
My old 7's, may it RIP, was a super sharp performer. I have found that hearing aid batteries are the zinc type that give off 1.35V. They might be a bit small in diameter, but I just wrap a bit of cardboard from a toilet roll around them to take up the extra room. Works like a charm and a lot cheaper than buying the special purpose 1.35V camera batteries. Which I suspect are just hearing aid batteries repackaged anyway.
The Wein cell 1.35v zinc-air will drop right in.It's the same size as the old mercury battery that it replaced.In the camera it will last about a year.Unopened in the package,about 8-10 years. I have two Hi-matic 7s cameras and also a srt 201 that I use this battery with great results.
I'm not a complete idiot.....some parts are missing!
Also, go to www.criscam.com The sell an MR-9 that is inserted into the battery compartment and a battery is inserted into that compartment. I had a Rollei 35 and used a recommended battery replacement for the Mercury. It did not work well. The voltage was too high and the meter readings were 2 to 3 stops off. With the MR-9 the readings are correct. Also, I have been informed using the wrong voltage can damage the meter. I don't know if tht is true.