That's interesting. Are you using V2 batteries with the V4L cartos? Wondering, whether your V4Ls the Cool Cart or Wow, prefills or filling yourself?
I just find the V2 cartos hold more juice and don't burn up as much. I've tried both the standard and longer cartos from V4L without much luck. I've tried them on both V4L & V2 batteries. I seem to burn them up quicker with a manual battery compared to an auto. I'm sure it's just me doing something wrong, but I just go with whatever works. I'm not knocking V4L as a company, their website, batteries and customer service are all top notch.
Perth, WA here *waves*