Shimano SM-BTC1 External Battery Case For SM-BTR2 - Bottle Cage MountShimano SM BTC1 External Battery Case For SM BTR2 Bottle Cage Mount If you cannot place the BT DN110 Internal Battery in your bike's frame you have two options: either use the BM DN100 external battery mount and the SM BTR1 battery, or use the SM BTC1 external mount for the internal battery. In most cases using the SM BTC1 is the better option. It has several advantages: You can use it with both SM BTR2 (previous internal battery) and the newer BT