I had an 03 Civic Hybrid that I got rid of in Jan. I had 0 gauge wire coming off the rinky dink OEM battery into a distribution. From there, out went 3 runs of 4 gauge to a Kenwood X4R and 2 X1R's. The battery back was replaced a few years ago and and it was needing replaced again soon so I ended up getting rid of it while I still could. I never really listened to it loud so I am not sure how much current was being drawn. The only time it kinda sucked was in the summer months when the AC was always running and the battery back would take forever to charge up.
My company had serious problems of certain newer hybrids when they tried to put two-way radios and other low current draw electronics in. One of them, not sure if it was a Prius, or Volt, or what, could detect the newly installed equipment and refused to motivate until it was all removed. Maybe it was just having a bad day? Not sure they ever figured out a way around it because employees that don't need the radio are driving them and the guys that need the radios are driving the old cars still.