Ubuntu thinks battery has no change, but windows detects it as fully charged

I have Windows and Ubuntu (20.04.6, kernel 5.4.0-144-generic) dual boot on an HP Spectre x360 laptop. A couple of months ago I replaced the battery with a non-official one as the old battery had lost capacity, which all worked fine. Then about a week ago Ubuntu suddenly stopped detecting the battery as charged, it always shows the empty battery symbol with 'Estimating...', and the laptop will shut down after a few seconds when not plugged in. Also, when I first turn on the laptop, I get an official warning from HP that the battery has no capacity, see image.

However, windows detects the battery charge absolutely fine, and everything works totally as normal on it (I can run it for hours on battery power), so I know that this is not a problem with the battery itself. Somehow the HP battery detection mechanism and Ubuntu are misreading things, but Windows isn't. Anyone have any ideas of how to fix it?

Things I have tried:

• Resetting the power manager as per this answer

There are a few key things to understand here.

First, this message does not appear to be coming from Ubuntu. It may be in HP's BIOS. Maybe the reason it doesn't appear when you boot windows is due to Windows' fast boot feature or something.

Secondly, when Windows is reporting that the battery is fully charged it is reporting on something different. This is the difference between battery charge and battery usable capacity. A battery can be 100% charged, but deterioration since manufacturer could mean that at 100% charge it's only around 60% as much as when the battery was new. That's the difference between charge level and usable capacity level.

So, this message is indicating that the usable capacity of the battery has dropped, to such a degree that it's indicative of poor performance of the battery and possible continuing deterioration, so it should be replaced to return to best operation.

However, you also said that the battery was replaced with an aftermarket (ie, non-HP) battery.

This means that all bets are off in regard to the usable capacity rating, and you can't trust that what it's telling you is accurate or is just a result of the aftermarket battery not confirming to the same way of reporting things as an official battery. So there is not necessarily cause for concern.

The non-official battery may have a poorer capacity than the original (and may not even live up to its own claimed capacity) but this doesn't mean it's due to damage or degradation, and either way, your laptop has no way of measuring this properly as it can only trust what it knows about the battery, and the battery is pretending to be something it isn't.

Some aftermarket batteries do a better job than others about reporting information to the host computer, but you don't have assurance.

As long as the battery is working to satisfy you, there's not necessarily any problem at all. Though, if this error message is coming repeatedly and that's annoying you, then you probably should contact whoever sold you that battery as you ought to expect that even if a battery is not fully compatible or doesn't report its usable capacity correctly, it should at minimum not result in consistent error messages every boot!