Almost every sailmaker had thier own design for the width and method of securing the battens. If the sail is old it is likely an elastic piece at the inboard end so you can push it beyond the leech of the sail, move it over to the closed side of the pocket, and the elastic will keep it in tension against the closed portion of the pocket along the leech.
If the elastic has given out you need to have the pocket rebuilt-preferably by a sailmaker.
The width is not really that important when you replace battens as long as it fits inside the pocket. Length and stiffness are more important.
Take it a sailmaker for repair, but if the sail is 15-20 years old, it may not be worth investing much money into..
Cheers,
S
