repair broken batton

About the only way I could think of is to sleeve it with some carbon tube that will slide over the top, maybe 10mm of it and all stuck together with Araldite. Seeing as though the tube section is designed to not bend it won't be an issue with changing the bend curve.

Carbon tube is easy enough to get at hobby shops etc but I dunno about that big.

You could possibly sleeve it internally but it is still pretty large carbon tube required.
Maybe some solid fibreglass rod about 100mm long, from a fishing rod blank or CB aerial?

I'd just get new battens, sail repairers and WS shops will have secondhand ones

I broke one recently. Sleeved it on the inside with about 40mm length of dowel. Tapered (sandpaper) the thickness of the batten either side of the join and wrapped in epoxy/carbon fibre. Wrapped it in shrink wrap and hit it with a hot air gun to squirt out excess resin. Make sure it's straight as the glue goes off. Sanded the lumps off. Still going OK, had it out today.

jobs done thanks fellows sleeved it with some alloy tube .I thought about a wooden dowel but the timber would expand in water so i went with alloy i already had ,glued it into place with super glue as mark reffered to that as the agent on formula battons thread.It helped i made a tight fit needed to be glued half at a time so i could push together, glassed around outside the heat shrink was a geat idea & i had some to fit for that too .Now all i got too do is test it .

should have clarified its internally sleeved and i hope it wont break & i wont be taking it out in the surf again i will wait for more wind & use my wave sails. Its a learning curve punched out alright other days with it might have got a bit ambitous there just wasnt enough wind