The Shimano E-Tube Internal Battery SM-BTR2 fits certain seat posts like the Pro Vibe, Pro PLT, and Pro Vibe 7S designed for an internal battery. It is a bit lighter than the external battery, and it helps to give your bike a clean look. The battery is charged with a USB power adapter (SM-USB1) through port on EW90-A/B cockpit junction box or SC-705 display unit so there is no need to remove the battery for charging. It has about the same long battery life as the external battery.
All Di2 components on the bicycle require the same firmware version. Using Di2 components with different firmware versions may cause malfunctions. Use Di2 system checker to update component firmware from http://e-tubeproject.shimano.com/