I'm pretty sure I read an Apple document about the best practice for the battery type used in the new MacBook but I can't find a link right now. Anyway from memory it said pretty much what Zhenya says: Ideally you should avoid ever letting it run down to empty, and you should avoid keeping at 100% all the time too. The ideal range seems to be to always hover around half full. In practice though, I suppose a good strategy might be to charge it fully, let it run down to 50% or lower, charge again (while still using it if you want), repeat. Depending on how you get about your day, this might mean taking a charger around with you. But if like me you find that you get home and it's still not anywhere below 70%, I have plenty of margin left over to then get it to charge back up again in the evening.