I am totally new at this but really like it so far. Other than needing new juices & a PCC! I ordered 3 510's 2 from cignot & 1 from widow bead. All went really well & they shipped ultra fast!! I also got juice from tasty vaper (spiced rum) really good! still waiting for Ms T...anyway one of my batteries is smooth on the inside & the other 2 look like they have like a screw type head on the inside...? Is there a difference??