How to properly charge li-ion from a smartphone (3.8v)?

Question

Do it yourself

We got almost free of charge 6 li-ion batteries new from a smartphone (Samsung). Seems like the originals. On the batteries it is written not as usual 3.7v, namely 3.8, and the max charge threshold is 4.35v.
I want to make a power bank out of them. But the question arose, do they really need to be charged up to 4.35v? And what will happen if I charge them up to 4.2v? Will they deteriorate and how much will they lose in capacity? Datasheet not found. I plan to parallelize all 6 of them and charge 1-2a with current from the charge module, which only charges up to 4.2v ...

Answer 1

I would put one charger per bank and limit the charge current (by soldering a resistor, information is easily googled) at the level of 0.5 C (For example, with a capacity of one battery 3000 mAh - 600 mA ). Fortunately, they are inexpensive, especially if you take it loose for your fee.
Otherwise, for example, with a normal desire to parallelize 2-3 chargers for a current of 2-3 A , we charge the package, 5 out of 6 have already been charged, and the last bank will suffer. Although you need to look at the datasheet, what they can do at all, perhaps this is a regular situation.

Answer 2

up to 4.2 nothing bad will happen. capacity will not be lost. But it will not work in parallel to charge. if the batteries themselves have protection, then just at one moment one bank will not be charged and the charger will stop charging all the banks. and if there is no protection, then you can just break the Akum (and even blow it up).
you need to take a balancing fee. and it is for 6 cans in your case. for example https://aliexpress.ru/wholesale?catId=0&initiative...

Answer 3

something like this

Answer 4

If you make a power bank, you can connect everything in parallel.
Of course, you don’t need to turn off the protection, it will not allow the battery to go into overdischarge, because. the power bank board will try to discharge them below 3.8 volts and the battery protection will not allow this.
The approximate charging current can be determined by googling the phone model, if they are from a modern smart with fast charging, then the current for each can be more than 1 ampere.
Therefore, it is worth choosing the most powerful power bank board so as not to wait painfully for a day until it is charged with a weak current.