Disassembly of cheap 18650 battery
I recently tested a 5000mAh rated battery, but it was only 1000mAh. After the review I was asked if there was a small battery inside or something else, i.e. would I please open it up and check it.
Today it was nice weather and I did it (The nice weather is important, because this is an outdoor job).
I decided to use a tube cutter for it. It is easy to open a battery this way, but as I also found out, cut a little bit too deep and I short the battery. There is no risk of explosion, because the battery is already open, but it do get hot (See below).
The battery does look normal (no small battery inside).
Lets take a closer look at the top. It has vent holes below the white disc.
But more surprising is it that the button top is part of the battery, usual batteries are manufactured with flat top.
Here I have removed the top from the can. In the battery all the can is the minus pole and the top is the plus pole. The red ring works as electric isolation between them and as seal.
The metal foil on the back of the top is the pressure seal. I.e. if the pressure inside the battery gets very high, this seal will break (Hopefully) and let the pressure out through the vent holes, instead of the battery exploding.
Usual this pressure seal is a CID (Current Interrupt Device), that will also break the connection to the plus pole in addition to venting, but not in this battery.
Batteries does usual have a PTC (Positive Temperature Coefficient Resistor) in the top, to protect it against shorts.
I cannot see any in this battery.
A closer look at the body of the battery shows a normal battery construction. I could not get it out.
Here I have removed the bottom of the battery and a bit more of the actual battery construction can be seen.
Another 1000mAh battery
I have once before tested a 5000mAh rated battery with 1000mAh in it, lets compare construction.
Ouch, I did cut to deep and shorted the battery.
It looks like there is a second wrapper below the first one.
Bingo, anybody know what factory this is?
It says IMR, it might even be correct, because this battery does handle load pretty well.
After some cooling time I could work with it again. It looks like nearly the same construction (The blue washer was also present in the other battery, but I did not get a picture of it).
Only change is that the plus connection is welded to a intermediate plate and not directly to the pressure seal foil.
This look like the first battery.
Here I have unwinded a bit of the foil, it has four layers.
This is one electrode of the battery, the black stuff is the actual battery chemicals.
The foil is coated on both sides.
The other electrode of the battery, the black stuff is again the actual battery chemicals.
The foil is coated on both sides.
The separator, there are two of these. They must provide electric isolation between the two electrodes, but at the same time allow chemical processes through the foil.
Conclusion
Both batteries looks fairly normal, but cheap. The safety is on the low side with no PTC and CID.
I do not know the reason for the low capacity, but a guesses could be that the foil and electrodes are thicker than usual and the actual battery chemicals are a very cheap type, maybe with a thinner coating than usual.
My guess is that these battery are made on a dedicated production line and only sold as flashlight/vapor batteries. I.e. they are neither old batteries nor second hand batteries, but simply made as cheap as possible.
Notes
Review of GTL 18650 5000mAh (Blue)
Review of UltraFire TR18650 5000mAh (Blue)
How is a protected LiIon battery constructed
Thanks HKJ, that is a sort of teardown that not many of us dare to do, and good pictures :-) . I have a few of these Ultrafire batteries that came with a headlamp, same poor capacity as these, still undecided what to do with them...
Have to love them, dedicated production line to manufacture complete worthless crap. No PTC or CID. 
Nice breakdown, these are surprisingly better than i was expecting.
This is from a RIDGID 12V pack that died early.
And another RIDGID pack, this time a 10 cell 18V pack. It seems these older packs all used these LS Chinese cells, and they were not that good. That dark area is where one of the cells leaked out. Perhaps this cheap “5000” cell used rejects or even recycled cells.
I doubt it, the cells looks new and they have button top.
Usual industrial cells has flat top, they are much easier to weld a connection on when making battery packs.
I have opened many laptop packs and tool packs. Spent cells can look brand new.
I made 2 assumptions concerning the LS cell.
Firstly I assumed that the underlying wrapper is legit and because it says “IMR”, it is truly an IMR.
Secondly I’m assuming that ALL IMRs would be manufactured with flat top because any cell that can deliver the kinds of Amps that IMRs can deliver would be spot welded into a pack, and not rely on a button top for a physical and electrical connection.
So my conclusion was that the LS cell was a re-wrap of a flat top recycled cell with a button top added or perhaps a re-wrap of a NOS cell.
If the button top is installed under the original LS wrapper, then my assumption about ALL IMRs being flat top is wrong.
Are you saying the button top is under the original LS wrapper?
But they will have traces from the welding, none of these cells had that.
And as I wrote, the cell does handle high load (At least to 5A) well (The other cell does not).
I did not check the one I disassembled, but I have checked another one, there the button top is welded on, i.e. it looks like the GTL is an original flat top cell, but the UltraFire is definitely not.
Nice for the teardown, HKJ! 8)
Thank you for the informative report HKJ. I don’t mind the small capacity so much, I could take 2 maybe. The safety worries me, though.
Also, do you haveany idea why cheap batteries charge so fast above 4.1 V or so when new?
I may have found some higher capacity cheap 18650’s but we’ll see. Need to use them.
i just did the same to some orange ultrafire 16340.
like 220mah at 500ma!.
total junk.
one has .57 esr and the other .31.thats 570mohms over 1/2 ohm!
total garbage.
there is no ptc or burst disc either.
so the vents in the top plate mean nothing.
now you know why the violent explosions when these fail.
Neat teardown. I had no idea that lithium ion batteries had a big roll of foil inside. Kind of interesting to see inside. 
Today most batteries are made that way.