So you have more energy and therefore the M8 can work for a long time before you have to recharge it again. It's the amount of energy you can use, not how much energy is used at the same time!
Compare it to a 1 liter and a 2 liter water bottle: You can drink the same amount of water in the same amount of time from both bottles ... but you can drink longer from the 2 liter bottle, because there is more water in it
