Saturday, February 24, 2018

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

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?

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