It's not a good idea. You'd have to watch it like a hawk - it could dangerously overcharge the cells and probably has. They'll discharge just fine but might be dangerous to recharge.
If any of the cells are above 4.3V after standing I'd treat them as single-use cells.
No, please don't do that. If you have a good grasp of how a battery charger controls the voltage/current during a charge cycle then you can pretty safely rig up something that more or less duplicates what a charger does, but just by asking this question that's a pretty good indication you don't understand it well enough yet.
Get it wrong and at best you'll damage the cells, at worst you'll start a fire and end up in the hospital.
ok can i use this then ? constant current and constant volt convertor i have used it as a constant current source for 5x XML in my Bicycle lights powered by 3s3p 18650 cells and it worked wonders
this is some of it’s Feature:
Output voltage: 12-35V (adjustable)
Output current range :0.5-5A (100W MAX) (continuously adjustable)
1. Step-up structure, Wide input voltage range (input less than output)
2. Constant current and voltage, Used to drive high power LEDs, and to charge the battery
3. Efficiency as high as 92%
4. Can be used for laptop power supply (voltage 16-20V)
5. Even the Step-up structure breakdown, Will not damage equipment, security design
6. With input reverse and undervoltage protection
7. Aluminum shell potting design, shockproof, Waterproof, Heat-Sink, harsh environments adaptable
8. Pluggable terminal design, easy assembly and disassembly, wiring more convenient
9. Can be Parallel work in power is not enough occasions
Don’t use that for charging either, li ion needs a charger with the correct algorithm to not overcharge a battery, you should look for a charger such as:
since you already used a bad method and overcharged your batteries you should seriously consider getting rid of them and replacing them because they are now an explosion hazard
If you have a DC supply, and can set it to a fixed open circuit voltage of 4.21-4.22v, and the current can be limited to a safe range, then it's pretty safe to use. But it'll take much longer than a proper charger that follows the correct algorithm.
In the CV phase, it should really be maintaining a fixed voltage across the cell of 4.21-4.22v, to do that will require a higher open circuit voltage. As the cell charges and its voltage rises, it'll require less voltage from the charger to maintain that target 4.21-4.22v. Unless you want to babysit the charger and 'drive' it manually, constantly monitoring volts/amps and adjusting it the whole time, just buy a charger that does it properly.