Hi,
Ditto what Whiteymorange said about the Hi-Matic F - the Hi-Matic E also uses the 640 battery and has the same issues. The 640s are huge, and when they go, they really screw up the wiring.
However, if you have one that works, the best adapter I've found is the one made by Joe Wolff - The Yashica Guy. Here's a link:
http://www.yashica-guy.com/document/px640converter.html
It's around ten dollars and Joe uses the proceeds to keep up his excellent website (for Yashica RFs). It uses a modern CR1/3N photo lithium battery, commonly available, that gives good, long service for these battery hogs. If you decide to get one of these, be sure and mention on the PayPal form what camera you are using it for, or Joe will cancel the order and chide you for not following directions.
Once you have the camera powered up and ready to go, be sure to keep the lens cap on it when not in use, or, better yet, remove the batteries.
I like both the E and the F but they are rather trying cameras to keep running, especially the complex E. I use the F as a hiking/cycling grab-and-go shooter as it is small, simple and sturdy and the exposure control (on both cameras, actually) is remarkably accurate - good enough for slide film.
Mike