Lithium Ion batteries offer three advantages over sealed lead-acid.
Weight: For equivalent capacity, a Lithium Ion battery weighs a half to a third as much as a lead-acid.
Durability: A lead acid battery is good for up to 300 recharges. A Lithium Ion is good for up to 1000 recharges.
Lifetime Performance: A Lead Acid battery starts to deteriorate from new, with the range travelled slowly diminishing over time. Lithium Ion performance will stay stable throughout its lifespan.