I recently found a dead laptop battery and disassembled it, found 6 batteries of CGR18650. So when I checked with them my multimeter, they had quite bit of voltage. So I decided to charge them, since I didn't want to spend money for a charger, I decided to make one. found This, I made it and now I'm able to charge my batteries. I'm watching charging current using my multimeter. So I found LM339N voltage comparator IC inside a broken power-supply and the IC is working.
So how do I modify my charging circuit with LM339N, I'm not an expert in electronics. So my knowledge is limited. Since I don't want my multimeter to be connected with the battery to measure current, I want to make some led bulbs glow when the charging is completed.