I was looking at 'power bank' circuit boards on Aliexpress, the kind that you add to a 18650 cell to make a basic 5V in/out supply. I noticed they all seemed to be lacking any kind of temperature sensing.
Most serious BMSes come with some kind of temperature sensor, so they can kill the charge current if the temperature rises too much. Is this necessary for a single lithium ion 18650?
I know about failure modes of packs where a cell goes short circuit in a parallel group, causing the other cells to discharge through it. Or a cell in a series group has a bit less capacity and ends up reverse biased. These events might cause damage if the charger continues to pump current through the battery.
But neither single-cell 18650 charging boards, nor 18650 protection circuits, appear to have temperature sensing. So is it safe to run a single cell without it?