How to charge Performante/huracan battery?

[littletiger]

I remove the protection panel in the luggage compartment and I can see the positive and negative terminals. What should I do next? I know I should connect the red clamp to the positive terminal/pole but what about the black clamp? I googled and got two different opinions. The instruction enclosed in the battery charger says connect the other clamp to the chassis, far from the battery and the fuel line. But firstly there is not too much pace around unless I take the whole luggage compartment out. Second I can see R8 owners on YouTube just connect the black clamp to negative terminal directly. Does anyone have the experience using the clamp to charge the battery in HURACAN please? Thanks for your input.