The Shimano SM-BTR2 is a rechargeable 7.4V lithium-ion internal battery designed specifically for Shimano Di2 electronic shifting systems. With a rated capacity of 500mAh and a weight of about 50g, this battery is intended for concealed installation inside a bike frame, such as within the seatpost, seat tube, or down tube, providing a clean, protected setup for road, gravel, and mountain bikes.

This battery is ideal for cyclists seeking a hidden installation and reliable power for their Di2 drivetrain. It is compatible with most Shimano Di2 systems that support the E-Tube junction system, but lacks compatibility with newer wireless units and some displays, so upgrading may be necessary for advanced features or future-proofing.

The SM-BTR2 delivers a dependable range, supporting about 600–1,500 miles between charges depending on usage, with a typical average of 1,000 miles. Charging is done via the Shimano SM-BCR2 charger connected to the Junction (A) box, taking about 1.5 hours for a full charge. This battery is particularly suited for those who value simplicity, hidden installation, and reliability. It is not compatible with Synchro Shift, nor with newer wireless units like EW-WU111/EW-WU101 or displays such as SC-MT800/SC-M9051. However, it will work with the older SM-EWW01 wireless unit (ANT only) and SC-M9050 display. For buyers looking to keep an older Di2 system running or seeking a hidden, robust power solution, the SM-BTR2 remains a practical choice.