Life span of a battery is important in case you want to own the battery and purchase it for life. But maybe this requires different thinking, a few scenarios: a) http://www.betterplace.com/ they own the battery and recharge it for you. So in that scenario you don't care about lifespan. Price of the battery is more important and of course how many millage. b) If the lifespan is 3x times worse then current Li-Ion, but price would be 10x less who care about it, Li-Ion batteries only last 8 years anyway. so you just replace the battery with a new one. Just the same as bringing in your car for a maintenance checkup.