With the release of the semi-wireless DURA-ACE R9250 groupset Shimano will also introduce a new battery, BT-DN300. This battery was mentioned in FCC documents, as well as the upcoming RD-R9250 rear derailleur.
Not much is known about the new battery at this time, but the 300 in the name is no coincidence. It'll connect to the rest of the Di2 system using the EW-SD300 wires.
Will it be backwards compatible? I don't know.
Will it still be a seatpost battery? I don't know. The battery pictured on this page is the previous generation BT-DN110.
Details & Specifications
|Shimano model number:||BT-DN300|
|E-Tube Port type:||SD300|
|Component series:||DURA-ACE R9250 (Road)|