One trick I did with my H-18 batten strings was to put stop knots in them to keep them from pulling loose. Once I measured out the sail, I'd put a stop knot (on the loose side of the string, just outside the batten cap) where my usual setting was so I could easily get the same setting again after releasing the battens after each sail. For less tight battens, I found that I could still set to the knot, just tighten it up to the knot (there usually wasn't enough tension at that setting to pull them loose) - sometimes I'd add a second knot for the looser setting. Alternative to the stop knot for repeatable settings would be to mark the string, but again, the knots kept things from pulling through/loose.

Additional - I'm assuming you have the batten end caps with the v-jam to hold the strings, above advice is for that...