In the end I found it was the cam itself that had broken, the batten entry point had warped allowing the batten to pop out - the batten itself was fine.
According to the guys at my club, this is a well known problem, and the cam has been replaced (by Tushingham). This was also described by someone unregistered earlier in this thread.
The new cam has rollers on the outer edges instead of the inside of the curve, and is reputed to be better. I've only used it once since, in fairly benign conditions, so I can't be sure the problem is completely fixed.
It does make the sail harder to rig though ...
I've no experience of the Ezzy Infinity I'm afraid ...