I will answer the question with questions..

What size sail?
How much roach on the sail?
And if so where abouts on the sail is it? Top, mid or bottom
What is the aspect ratio of the sail? Tall & thin or short & stout?
Is the sail intended for light or strong winds?
How mush twist do you want?
Is the mast soft or stiff?
Do you want the battens to force shape in or flatten the sail?
What are the battens going to be made of?
Loose footed sail or fitted to the boom?

You may not be able to answer ALL the questions but work through it it will determine the answer.

If you are are after a general class 5 sail the development has been done (no point in reinventing the wheel ...so to speak)
The class 5 specs limit the mast height and the pocket size and to achieve the max class size there needs to be a med. amount of roach in the leach area.
The head of class 5 sails has changed over the years to a more rounded top and with more rake in the mast this design tends to dictate the number of battens and how they are used.
My suggestion is have a look at current pics of class 5's in the NALSA (USA), British or European sailing sites.

Amount of battens seem to range from 5 to 9 in class 5.
I have 3 sails
9 batterns - British sail
6 battens - NZ sail
5 batterns - most popular in aus.

Class5 promo are limited to 5 batterns I think

Most international class5 use 8 battens as for the best option I prefer my NZ sail for all round performance.

Most of these sails can be viewed in the photo section.

Cheers

au