Latest opinion is that any time spent fully charged damages a lipo. This time is cumulative so a littel here and there along th way adds up over time. The one thing I've not seen addressed is how this damage manifests itself.

But to your question, either charge before you use them or charge to a slightly lower voltage like 4.1v. The lower voltage is not damaging and I doubt you'll notice the difference. Personally, I charge before I use them and storage charge them after I use them.