Reciever setup.

Hi, I am new to this Brushless setup as I hve always ran Nitro.

I am in the middle of converting a Truggy to Brushless.

So this might seam like a basic silly question, but i have to ask.

I have the Truggy Tekin 1700 and RX8 combo
I have 5800mah 5s Lipo
Reciever is a Futaba 3PK 2.4

Now for the silly question.
Do I need an extra battery to plug into the reciever?
I know the steering goes into 1
I know the RX8 control goes into 2
But that leave the Battery hole empty.

Hope this makes sense.