I read the datasheets and I don't see why they wouldn't work together, but i'm no expert.
the mosfet is a SSM3J352F,LF , the opAmp is LMV321LICT , I got them both from digikey. They are super small and were tricky to weld, I can't exclude that I fried them when I welded. I did 3 lamps and they all show the same behavior, and I think it's unlikely that they are all fried, specially as they work when the battery is charged.
should I put a resistor to the opAmp VCC pin? i'm afraid it will decrease even more the voltage...
concerning the driver it is a 3W LED driver from aliexpress : https://fr.aliexpress.com/item/3W-LED-driver-16MM-DC3-7V-1-Mode-LED-Flashlight-Driver-for-CREE-XRE-Q5-XPE/32627605064.html?spm=a2g0s.90423184.108.40.2064f6c37kYHKsp
does anybody have another idea for this circuit? something energy efficient to get the battery last the longest possible.
Thank you very much for your help