Cant do synchro shift without this battery, and its worth the upgrade just to get synchro shift. I'm not a lazy shifter but it is convenient in a race to not have to think about the gearingcross chaining as you meet hills. Just shift!
Does what it's supposed to...but the real joy of the new DN110 (vs BTN2) is the ability to allow the slimmer D-Fly replacement Di2 transmitter AND the ability to support syncroshift on Ultegra Di2 (as of 32017) with firmware upgrades (you are regularly upgrading your firmware, right?).
I replaced my older BTN2. I was upgrading my derailer and I wanted the features on the e-tube app so figured now was the time. Straightforward unplug and plug. It is not clearly stated so I was confused if the new battery alone support blue tooth or I needed to add the EW-WU111. This is not the case. The BT-DN110 WILL pair with your phone and you can use the etube app. This DOES NOT require the EW-WU111.
Also, the new batteryderailer combo supports synchro shift which I unexpectedly like very much.