Shimano SM-BTR2 Di2 Battery - $199.99

The long-awaited internal battery for Shimano's Di2 electronic groupsets is here. Designed as an alternative to the SM-BTR1-67 Battery, the new cylindrically-shaped SM-BTR2 Di2 Battery was engineered to reside either within the seatpost, seat tube or down tube of your bike. Besides the obviously different shape and mounting location of the new battery, Shimano carried over the proven functionality of the externally mounted battery to this new design. It's still a fully-sealed, 7.4-volt lithium-ion rechargeable unit and provides the same battery life as the external version, but it now comes in at roughly 15g lighter and stays concealed from elements for better protection and improved aesthetics. Battery life for the SM-BTR2 Di2 is similar to the externally-mounted battery. For the prospective Di2 buyer, know this: running out of juice is nearly impossible. Besides the long battery life and short charges, there is a service light integrated into a module that is part of the shift wire near where it exits the tape under the handlebar. Holding one of the shift paddles down for a few seconds will activate the indicator light. When the light is green, it is fully charged. At 50% charge, it will start flashing green. At 25% charge, it will turn solid red. It will flash red when the battery is critically low. The Di2 battery lasts from between 600 to 1,500 miles between charges. You can expect that lots of shifting in cold, cold weather will result in shorter battery life, but we've found that 1,000 miles is an average interval. There is no "charge memory" in the battery, so you can recharge it as often as you like, though Shimano recommends once a week or so if you're a daily rider. The battery can go 300 charge cycles at 100% integrity; charging once a week means almost six years. Please note: Shimano made charging the new internal battery a straightforward affair once you have the compatible parts. - $199.99