How do laptop batteries and chargers communicate with the laptop and what do they 'say'?

Question

I have an HP laptop that does not like its new after-market battery (original parts are no longer in production). I am having a curious problem in that when the battery finishes charging, that if the AC adapter lost power, the computer will shut down immediately. However if the power connector is pulled out of the laptop itself, it doesn't.

What different information might the laptop be receiving from the adapter that it can tell the difference between losing AC and being unplugged at the connector. I can see the HP uses a 3 pin connector and have read that it is effectively a dual layer coax cable so I assume the centre pin is for communication.

I have tested many different chargers and found that the effect is identical with all, and even tested across several laptops. The common denominator is the battery. Batteries have many terminals, 8 in this case, so the laptop and battery must communicate. The running assumption is that the battery is not correctly switching to discharge mode when AC power is lost, however the case is very specific.

What then is the communication protocols, standards etc. that are used in the charger <> laptop <> battery that might help me unpick this issue?

Answer 1

AFAIK the battery interface is not standardized, and each laptop manufacturer can implement its own proprietary interface. Aftermarket outfits have to reverse-engineer the interface.

Google "battery monitor ic" and you can read about chips from STM, TI, Maxim et cetera used in battery packs, e.g.

http://www.ti.com/lit/ds/symlink/bq2019.pdf

https://www.ablic.com/en/doc/datasheet/battery_protection/S8255A_E.pdf

https://www.st.com/en/power-management/battery-fuel-gauge.html

The communications channel between the battery monitor and host need only be a single wire (with ground) serial interface, and is typically based on I2C.

What then is the communication protocols, standards etc. that are used in the charger <> laptop <> battery that might help me unpick this issue?

Charging and discharging lithium-ion batteries is not a trivial topic, and involves safety concerns.
If the engineers at the after-market battery manufacturer could not successfully clone a HP laptop battery pack, then an end-user is not likely to complete that task.

Answer 2

Dell as example: https://hackaday.com/2014/03/03/hacking-dell-laptop-charger-identification/ Its a one line communication. Thats why the pc knows how much power the adapter has. Correct me if i am wrong.