So I use an Asus Vivobook and I finally realized the reason the battery was still running down - a duh moment - the power cable was only half-plugged into the laptop’s port.
But…
For many minutes, the laptop had hovered at exactly 73% power in the battery - no gain, no loss. Wondering how this works? It is still there - seemingly permanently at 73% no matter what. Even putting the cable fully into the laptop port has made no difference. It’s been at 73% for an hour now.
Is leaving the cable half-plugged into the port (as opposed to fully plugged in) bad for the laptop and/or battery?
Why is the battery not going up or down in power level?
There’s a few possibilities. First off, the OS doesn’t know the internal state of the power management circuitry, it simply signals that it is charging or not.
The power adapter could have separate wires for charging and power, and only the power connection was made. This was more common many years ago, though, and most, likely all, modern laptops use a single connection.
It’s also possible the connection wasn’t good enough to supply enough current to charge and run. This would also cause a voltage drop across the connection, and likely localized heating.
Lastly, many power supplies contain an ID chip that is read by the laptop. If the power management circuitry can’t detect the chip it won’t draw full power. This is, IMO, the most likely reason. However, I don’t know which specific Vivobook you have and can’t see if your model has that.
Also, if the battery never resumes charging, even after restarting and replugging the power adapter, it probably means the battery is degraded. In that case, the half plugged adapter simply caused the laptop to run on battery and the latent battery degradation was made apparent by recharging.
All lithium ion batteries degrade with use and age, and always running on AC power and keeping the battery at 100% all the time is highly detrimental to battery wear.