Li-Ion 18650 Battery: Using Laptop Balancer for 12V Portable Device & Preventing Over-Discharge

I need to make a battery for a portable 12V device. I have a 18650 battery available with 3 laptop batteries (capacity during the measurement). When I take these batteries apart, I notice that there is a balancer inside.

Can I use this balancer to prevent excessive discharging of individual cells?

AVE ...

You can, but:
1. You need to know what layout it is made on and get a catalog note for it, which can be a big problem, because some layouts require NDA signing and are additionally secured with a password.
2. You need to reprogram the EEPROM with parameter settings, which requires a programmer for such memories or an SMBus interface to connect to the controller. The latter + password are needed in cases where the controller has no external memory.

Generally, for ~ 20 battery plates I have only 2-3 that could be reused ...

In summary, it is not enough to find the power supply (P + and P-) in the laptop battery and connect to it, because the laptop controls something there, and the "balancer" is a small driver that would have to be reprogrammed for another operation?

AVE ...

Exactly. These circuit boards in the batteries control the charging and discharging process, track the battery capacity and state of charge, monitor the temperature and generally care for the life of the cells. Sometimes the batteries "lose" capacity, because the control system has counted enough charging cycles to recognize that the cells have worn out even if it did not happen ...