Someone recently posted about having problems with a new light that they resolved by cleaning the ends of their battery. That had never occurred to me - but this evening I experienced the same thing.
A new Skilhunt H03 displayed a ‘low battery’ warning with a recently charged cell, and then shut down. The cell repeatedly tested 2.8 / 2.9 v., but the reading was erratic and not steady. On a hunch (and thanks to whoever posted about this a few days ago) I just gave both ends of the cell a brisk rub with a rough cloth, and sure enough - it tested 4.18 v.
The H03 is now running perfectly with that cell. The moral of the story? Give the ends of your cells a good rub down before you use them, especially if your light misbehaves.