Well, I had this Keeppower that had got a crushed button top and slightly damaged wrap so fancied having a look under the wrapper!
The wrapper is single layer, black, seems quite rubbery and not as brittle as the cheap wraps. Under the wrap is the circuit board, +ve strip with kapton tape, and a spot welded button top.
Protection circuit seems to have 3 x MOSFET in parallel which would help to reduce voltage drop across the protection circuit.
Can’t find any info about the control chip yet, I will update if I do.
Wrapper removed and label
Button spot welded, couldn’t get it off, the dent doesn’t seem to have damaged it.
Protection Circuit
MOSFETS cut and bent up to see the tracks.
All parts
I would like to identify the cell, markings are similar to ones I have seen on Sanyo NCR18650GA (edit Jan 2020, the supplier confirms it is that cell Keeppower are using)
My dodgy attempt to draw out the circuit, no guarantees its rights!
I bought this from 18650.uk earlier this year, so it should be the 2019 edition.
That is a good looking protected cell. No wonder they do work so well. I only have a couple and they are older versions, but have not given me any troubles.
I’ve been running it in the FT03 XHP 50 and not managed to trip the protection yet, I think it must step down before it trips. HKJ reviews has trip about 7A - 8A.
I can confirm the cell under the wrap is a Sanyo NCR18650GA. I tore one down to check them against their datasheet (which pulls a large amount from the Sanyo one) ran them back to back in testing to see if it was possible to determine whether or not they were using the same direct from factory quality that we purchase, or whether they were using factory seconds/ B Bin cells. They performed only marginally worse than what we know to be direct from factory cells, indicating that they might perhaps just be old (>1year from manufacturer) or just stored incorrectly at some point.
Its an unfortunate issue, yes. Im surprised that some of the larger wholesale businesses in the US haven’t already spotted and jumped on this. There’s a huge amount of room to be able to provide people with properly obtained, tested, verified and built cells at a fraction of the cost of the currently available ones. I’ve specifically used plain clear wraps from design stage so that customers can see exactly what they’re getting rather than coming up with some kind of “brand” for them.
Liionwholesale has its own brand (MJ1, GA and others) of protected cells and Illumn has a low cost protected MJ1 made by Keeppowers (but from Zeroair testing the protection circuit seems less performing than the more expensive counterparts)
G2Jk - appears to be a Seiko Battery Management IC, or a clone. There is no “G2JK” entry, but Google shows G2JK, G2JS, etc. So the last character code be a variant or temperature qualification code (Consumer, Industrial, Automotive, etc).