Shimano's Dura-Ace Di2 takes shifting to the next level. This amazing technology is powered by this small, light, high-output Lithium Ion battery that delivers reliable, long life even in the worst of conditions. Even while riding terrain that requires lots of shifting, the battery is capable of about 1,250 miles of use before requiring recharging (this takes 90 minutes). The battery includes a mount that easily attaches to the bottle cage bolts on your frame. And, the battery can be removed without tools for charging (charger sold separately).