Yes you can use your battery to directly power the camera using the ptap connecter on the battery. You'll need a cable like this https://www.amazon.com/dp/B07R1HXDLG/ref=cm_sw_r_sms_apa_i_0FFpEb970129B

The Pocket 6k can accept any voltage between12V uptto 20V. The battery puts out about 14.4V ( or less as it losses charge).

Others might be using plates because of additional power connections (some have power outputs with reduced voltage for other equipment like monitors). Or some older batterys don't have built in ptap connectors so a plate would be used to provide that connection. Their are also dummy plates which just hold the battery and they have mounting points to connect to a cage or rails.