Li-ion battery charging

Please I have some couple of 3.6v 3Ah cylindrical li-ion battery, but since I bought them, charging it became a huge problem. I first connected a single one to a 2A infinix phone charger (made in china. According to the ratings, it capable of adjusting output current and voltage to load)thinking that if it's capable of charging a 4Ah infinix phone battery then a 3Ah shouldn't be a problem.
Until I connected the battery directly to the charger output, after some time, i measured the output voltage of both the battery and the charger, the battery was not charging and the charger decreased it output voltage from 5v to 2v and was also giving me an unusual jolt in my finger. I concluded that the charger has damage. I tried it again with a similar charger, but this time a TECNO phone charger, but the same result.
I then found another SMPS charger 12v, 1.2A. In my desperation, I ignorantly implemented a '7805' regulator ic to drop the voltage to 5v(since using a smps to regulate a smps sounds absurd). When I connected the battery, I measured the charging current, and I was so surpries to see 2A.From a 1.2A(short circuit current) SMPS.
So please where did I went wrong and how can I charge my batteries before it damage.
Hello...I was likewise scanning for a Li-Ion battery security IC, to "separate" the BATT from the circuit in circumstances of under-
voltage (over-release) and over-voltage (over-charge). I discovered this IC model on Digikey: S-8241ABKMC-GBKT2G. This IC (S-8241ABKMC-GBKT2G) controls two MOSFETs who are associated between the Li-Ion battery and the circuit's capacity flexibly.

rigid flex pcb design for assembly guidelines
Hi anditechnovire,
you cannot use phone chargers or 7805 because they are constant voltage output. The charge of Li-Ion batteries requires a constant current source until the voltage reaches the typical value 4.1V (single cell).
At 4.1V the charge MUST be stopped ant the cell is fully charged. In case you go with the charge above 4.1V the cell can be damaged.
A simple scheme to make a constant current source for battery charging is the following:


The values of Rs, R1, R2 can be calculated for your application with the following formulas:


VOUT must be 4.1V (for a single cell charger) and it is determined from the ratio R2/R1.
IOUT is the current you want for use for charging, for example 2A. It is determined from RS.

The pictures and formulas above are taken from the LM317 datasheet.

I hope this help!