Is this a protection circuit?

[whc]

Just took apart what I thought was an unprotected 18650, though found the PCB in the image below, is that a protection circuit, that protects from over/under charge/discharge?

Here is the image, sorry for the low quality it is taken with my cell phone.

 

[MatajumotorS]

Yes, it is protection circuit.

 

[whc]

Yes, it is protection circuit.

But does it protect from overcharge/discharge, some protection circuits only protects from heat if I am not wrong (ICR)?

 

[MatajumotorS]

it protects against ower charge-discharge , BUT at moust low 2,75V and high level @ 4,35V is too low and too high.

In LI-ONs from dx upper level was exactly 4,20V but lower level still too low 2,75V (3,0V ar 2,95 would be perfect).

You can put lab psu instead of li-on to this circuit and measure on other side when it cuts off.

 

[Fallingwater]

Just took apart what I thought was an unprotected 18650

Why on Earth would you want to do that? Disassembling LiIon cells is very dangerous.