I want a mod that doesn't need a LiPO pack or series LiPOs but still has the run time capacity, therefor a dual battery 75C, or 75, fit my specs.. Just a preference. If I'm going to build a 250C I don't see the point of throttling it by running it less than 4S, not that I vape at anything, even close to, the maximum output of a 250C with a 4S. Just how I look at things. It still doesn't explain the failures I'm seeing and that is my biggest concern.
In fact I recently converted a couple of 250s to 75s running dual 18650s and the vape time is amazing compared to the 3S pack. The reason I converted them is that I got tired of changing LiPO packs every time they started swelling, from charging.