I have a doubt about what is the difference between BAT- and PACK- in this battery management system available in a github project: enter image description here

As I read in the datasheet of the BQ76920, the N-Channel FETs are for cell balancing and protection, and the R10 is for sensing overcurrent, so my doubt is, what is the purpose of having a connector for BAT+ and BAT-, and what is de purpose of having another connector with PACK+ and PACK-? Is PACK+ and PACK- a connector for connection of the load and the NCH FETs and resistor R10 performs the overcurrent and short circuit as mentioned in the datasheet?

And BAT+ and BAT- is a connector for charging the cells?

So do I have to charge the battery though the BAT+ and BAT- terminals?

Thank you


1 Answer 1


The BAT+ and BAT- are connected to the highest and lowest potential of the battery stack. The PACK+ and PACK- are connected to an external load or charger.

While BAT+ is directly connected to PACK+, the current on the low side connection from BAT- to PACK- is measured with a shunt resistor and can be blocked by turning of the corresponding charge/discharge MOSFET. So in essence, the battery stack is always connected to the BMS but the charger or load on PACK can be disconnected.

This has nothing to do with balancing FETs. Those switch on a resistor directly across a single cell to discharge individual cells when necessary. It appears that the IC internal balancing FETs are used here.

  • \$\begingroup\$ I understand, thank you! One more question please, what is the reason to have two connectors? the LOAD one and BAT one? that is something confusing for me. What should I connect to each one? Do I need to charge the battery through LOAD connector in the same way as connecting the load in that connector? and what about the BATT connector? \$\endgroup\$
    – imt_blake
    Commented Mar 28, 2023 at 16:50
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    \$\begingroup\$ Yes, you charge the battery through the LOAD connector. The BAT connector is connected to your battery. \$\endgroup\$ Commented Mar 28, 2023 at 17:03
  • \$\begingroup\$ I just saw that The BAT connector is just in case I have the battery pack considered in the design but only available the highest + and lowest - terminal, is that right? \$\endgroup\$
    – imt_blake
    Commented Mar 28, 2023 at 17:07
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    \$\begingroup\$ You will need to connect the highest and lowest potential of your battery to BAT+and BAT-. Otherwise the BMS will not be powered. \$\endgroup\$ Commented Mar 28, 2023 at 17:11
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    \$\begingroup\$ It is not sufficient to connect B1..B5. You also need to connect BAT+ and BAT-. There is no internal connection of B1 and BAT- or B5 and BAT+. You will need to wire those separately. If you look at the PCB picture you can also see why: B1...B5 are small wires that do not need to carry much current. BAT+ and BAT- need to carry the entire load current and also provide power for the BMS, 5V and 3.3V. \$\endgroup\$ Commented Mar 28, 2023 at 17:32

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