What is the most efficient way to output 5V from 18650 batteries?

Question

Batteries

A non-working power bank arrived from China, so I think I can insert a DC-DC 5V stabilizer instead of that circuit or somehow turn it into a working one. It has 3 18650 batteries.
In theory, 2 batteries will be 5-6V, you can stabilizer there. But the problem is with the protection against overdischarge. Or are they already protected? Written - with protection, but who knows.
And with charging, too, then it's not entirely clear - at least charge separately.

Answer 1

Connect the banks in parallel so as not to bother with balancing. To get 5 volts, use a step-up converter, like this: www.dx.com/p/usb-dc-1-5v-to-dc-5v-voltage-step-up-... Can also be found at 2 A output current, more expensive.
There are also ready-made modules for charging: www.dx.com/p/tp4056-1a-li-ion-battery-charging-mod...
The presence of protection on the battery is recognized by a blotch on one of the ends and a metal tape along the side of the can. If there is no protection, then it is also sold separately: www.dx.com/p/charge-discharge-protective-circuit-b...

Answer 2

I would suggest starting with studying the native scheme, and when a clear understanding of the principles of its operation appears, then all questions will disappear.
Without this, it will be possible to farm up to a self-explosion or fire.

Answer 3

Try something like this

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