So I started tinkering with arduino a couple of years ago. My background in electronics is that of a noob with a little hands on experience and little theory.

I've worked with 2 circuits that I tried to assemble following tutorials but failed miserably:

1. Amplifier using lm324 opamos all while only learning how opamps work. I sorta grasped the understanding but decided to move on.

2. Oscillator circuit using 3906 & 2222 transistors, resistors and capacitors. Originally the idea was to make a led flash on and off to keep a battery pack alive. Again I sorta got a grasp on how the circuit should work but couldn't get it working.

So I can sorta see how oscillator circuits and amplification circuits are common. Today I cracked open a solar mobile charger consisting of a solar panel, nine 18650 batteries and some circuitry.

Among the circuitry is a small strip board which I've seen in other mobile chargers which I believe is used to regulate the charging process. Here is the image below. Can someone explain in as layman terms as possible how it works and gradually move into the details?

 

It's a battery maintaining pcb, it monitors the charge of each cell and cuts off them off when fully charged or discharged to prevent explosion or fire. All the cells are in series.

 

Thanks. So i looked at the chips on that board and there are:

4 ME4435
and
1S8254AA

Googling shows that S8254AA is an IC specifically designed for battery protection from overcharge and over discharge. Venturing into the schmatics I noticed some opamps, which makes sense because from my failed attempt at a battery charging circuit, I remember it used 4 amps which you would set to "turn on" at different voltages depending on the resistors you added to them. And I know some opamps are used as comparators so I guess it makes sense to "sense" the battery voltage and based on which opamp "turns on", take action to charge a lot, charge a little or dont charge at all.

But when looking at the ME4435 I found some mosfet related entries and another one as an oscillator circuit oddly enough. What would an oscillator circuit be used for in this case?