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.
First of all, never connect a power supply directly to a Li battery. You have two option to charge your battery. The fastest way is to find and purchase a Li-charger "module" or a "power-bank module" which is designed exclusively for charging Li batteries. The second way is to use ICs designed to this purpose (like TP4054) and build your circuit (PCB) based on this IC.
Generally, a Lithium battery voltage ranges from 3.5v to 4.2v (Max). The charger's max voltage should be limited to 4.2volt and its current should be limited(depends on the charger and the battery). So in the middle of charging process, the charger's voltage might be lower than 4.2v to prevent from rushing current. Another feature of such a module or IC is that they stop charging if the battery is full, so it prevents from over/extra charging.
I have build this simple charger, and it works. more details on: http://danyk.cz/li-ion_en.html