31:T7ff,This is the one common item between Shimano's Dura-Ace and Ultegra Di2 groups -- the Di2 SM-BTR1-67 Battery. Call it Ultegra, call it Dura-Ace, but we'll call it the one you'll need. It's a rechargeable lithium-ion battery that mounts on a bracket designed to work with bottle cage mounts. The mount stays on the bike at all times, though the battery can be removed for charging.Everyone's first question is about battery life. Shimano sat back and watched Mavic on both its attempts at electronic shifting. Both their Zap and Mektronic groups were susceptible to surprise failure. In a nice gesture, Mavic designed the rear derailleur so that the rider could manually move the pulley cages to choose a gear to ride home in. And it happened all too often.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. One nice aspect to the electronics in the Ultegra Di2 kit is that the battery is in a sleep mode and not using any energy when you're not shifting. 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. Material: ,
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