I recently bought a Thrunite U1 charger which came with a Thrunite-branded 18650 cell.
Wanting to know what the cell was based on, I took the Thrunite PVC shrink wrap off to see what was underneath.
The outer wrapper was marked "3400mAh, 3.6v, 12.24wh" and "integrated battery overcharge/discharge protection circuits."
What I found just left me (and others) confused. Here are the before and after pics:
http://i.imgur.com/1y0R7WP.jpg
http://i.imgur.com/FtvSGII.jpg
It's clearly a Panasonic NCR18650B, but the section on top that's not wrapped with the rest of the cell doesn't resemble any other battery I've seen.
I didn't spot any kind of insulated metal strip running the length of the cell from positive terminal to the circuit which (ostensibly) would be on the bottom, as showcased on this page:
I believe that is the Protection Circuit at the +ve end, therefore there is no need for the metal strip running the length of the cell connecting the -ve to the +ve pole.
I have seen others with the Protection Circuit at the +ve pole, But it is rarely seen.
That actually makes a lot of sense. The bare metal casing of the cell is negative anyway, so both + and - are very close together at the top. It would be easy to get both connections to power your protection circuit without that strip, which is much safer. Wonder why more manufacturer’s don’t do it this way.
Out of curiosity I’ve cut the wrapper from “normal” protected cells before, like this KeepPower:
Definitely had the circuit on the bottom and a strip running the length.
