Hi Simon,

I have never had (permanent) warping on my sail battens (Dart 18, then home build wood/glass, now Fibrefoam) so far.
Be carefull with sanding battens, if the fibres are uncovered by resin, they really damage the sail. But yes the edge shouldn't be sharp of course. I have seen more than one sail torn in two at the batten pocket. Luckily it wasn't my sail.

Cheers,

Klaus