The battery connector is the connector at the right of the motherboard. Above the battery, there is a bridge connector which connects the mainboard with the sub board at the bottom. So remove both the cables. There is a slight adhesive below the battery. Cut through it with a plastic spudger and it will come out.

The sub board has the antenna terminals also and prior to removing the battery, the antenna cable needs to be removed as well. Gently disconnect the coaxial cable from both the motherboard and the sub board.