Fullspeed does not provide the target configuration to Betaflight devs and are maintaining theiro own branch of the Betaflight firmware. You have to download the HEX file from the FullSpeedRC website and upload it manually.
FULLSPEEDF411 Firmware Link: http://www.fullspeedrc.com/fsd-f411-flight-controller-for-fsd428-fsd435_p0162.html
GnB (Gaoneng) batteries are probably the best. I would suggest 550-650mAh 3S battery for this quad.
You can look look for GnB batteries on Banggood: https://www.banggood.com/search/gnb-3s.html?sbc=1&p=@K2800431511201401MH&cur_warehouse=CN or any other your preferred shop. If you are in US, then you can find them in the local (web)shops (PyroDrone, GoodventureDrones, Rotorgeeks, etc.)