On the mainboard of your Joy-Car you can make further configurations with the jumpers. Here you can deactivate the Speaker [SPK] and the battery voltage measurement [BAT] and thus activate pins P16 and P2 on the pin header of the mainboard. This way you can activate two more pins for your own development, if you need them.
To switch your Joy-Car on or off, you don‘t have to insert or remove the batteries again and again. You can easily disconnect the power supply via the on/off switch.
In the assembly instructions, you have already learned that you can connect the battery holder to the BAT terminal. However, if you should make your own modifications, you are not bound to the battery holder. Here it is good to know: You can connect any voltage source between 4.5-9V to the BAT terminal.