I find their table of advertised vs actual capacity to be misleadingly negative. They only discharged to 3v. 2.7 could be viewed as more standard. 2.5 is not unheard of. For example, the vapvell 4000 they said was around 3000. They even have a note that says that isn't a reasonable capacity estimate. And yet they still put the percentage and the number. As if they've falsely advertised. However, if you go to vapcell's graphs on their website, it all tracks. Feels out of scope for the report and shouldn't have been done

I went to vapcell's website, looked at their charts and specifications. I disagree with your assessment.

They specify 3800mAh minimum discharge at 0.2C for their 4000mAh cell. They don't show a discharge curve at 0.2C in their charts (would be 0.8A) but they do have a 1A discharge. When the 1A discharge curve reaches 3V, the energy discharged is right around 3800mAh.

Lumafield discharged at 0.2C, and they saw only 3055mAh.

Vapcell's site mostly shows high current discharge curves, where yes there is more capacity below 3V available, but with Li-ion at lower currents, the curve is very steep past 3V, not much more capacity left after that. And when you're discharging at high current you won't expect to get the full capacity, anyway.

I'll also take this time to point out lygte-info which is a treasure trove of battery tests.

[0] https://www.vapcelltech.com/h-pd-193.html

[1] https://www.lygte-info.dk/

It even says "Conservative discharge that would not extract maximum performance". A lot of electronics built for li-ion will not work <3V so it's a perfectly reasonable benchmark, especially to show the difference between brands.