So finally got my new mainsail up this weekend and went for a short sail. I was surprised to see that the top 3 battens (which are full length) have no method to retain them or tension them at the leach. They simply push into the batten box at the front and then the screws are tightened to clamp them in the box and hence sail/pocket. My sailmaker says this is the way he does them now. The bottom two battens- which are not full length- have the normal velcro strap to keep them in and tensioned. I thought the whole purpose of a batten was to push the leach away from the luff to avoid vertical creases maintain shape and allow a little bit of roach. How can it possibly do this when it is free floating at the leech? Naturally the sail sets horribly with lots of vertical creases as in the attached picture. Perhaps I didn't shove the battens into their boxes enough or I am totally misunderstanding something.

Would strongly suggest there must be a tensioning system "hidden" in the leech of the batten pocket, eg with an allen key activated threaded component which compresses the batten. Suggest you specifically discuss with the sailmaker. If it isn't at the leech it might be in the luff pocket system, with the leech securing the batten end somehow.

Some batten systems enter from the leech, others from the luff - all will have a tensioning system.

www.northsails.com/sailing/en/2022/01/what-you-should-know-about-your-battens-north-sails

So you're saying the batten pokes out of the leech of the sail?

Thanks guys for your answers. Yes I think the full battens should probably have been inserted from the slit under a piece of webbing behind the batten box near the luff rather than through the leach like I did it. I am on a friend's catamaran at Broughton Island for a week so I can't get back to my boat to have another go at them yet.