I have had a fair bit of experience with lithium batteries, as i used to race enduro bikes in night events using lithium powered lights. (not as much fun as chasing four legged things at night i must admit )
They are fanastic batteries in lots of ways- dont get me wrong, but what deben and the other companies dont tell you is lithium batteries loose 20-25% capacity every year (even when stored correctly), so effectivly this is how mush lamping time your going to loose, so a 4 hour battery will only last 2 hours in its second year. Also the temperature you store them has an effect on their