Created attachment 282193 [details]
acpidump

Hi Laurent, Are you running the latest firmware distributed by lenovo?

I think yes:

[   13.662480] thinkpad_acpi: ThinkPad BIOS N27ET34W (1.20 ), EC unknown

https://pcsupport.lenovo.com/be/fr/products/laptops-and-netbooks/thinkpad-t-series-laptops/thinkpad-t580-type-20l9-20la/downloads/ds502395

Not that I suspect that these errors are preventing upower to get the notification when the AC power is inserted/removed

Here's what's going on (for your information and for my future reference):

When the AC adapter is plugged/unplugged, _Q26 and _Q27 control methods attempt to index a package element out of bounds in the BRNS control method. The indices are from these operation region fields: BNTN and BRLV. These variables are values that are contained inside system memory.

Method (BRNS, 0, NotSerialized)
{
    Local0 = (\BRLV + 0x02)
    Local3 = \BNTN
    If (\_SB.PCI0.GFX0.DRDY)
    {
        Local2 = DerefOf (DerefOf (BRTB [Local3]) [Local0]) // Index out of bounds runtime error
        \_SB.PCI0.GFX0.AINT (0x01, Local2)
    }
}

I'm asking around internally to see if someone from Lenovo can fix it...

for what's worth.
I have the same issue:

2019-04-14T09:38:06.256739+02:00 linux-5q3o kernel: [   10.210587] thinkpad_acpi: ThinkPad BIOS N27ET34W (1.20 ), EC unknown
2019-04-14T09:38:06.256742+02:00 linux-5q3o kernel: [   10.210589] thinkpad_acpi: Lenovo ThinkPad T580, model 20L9CTO1WW


2019-04-15T20:04:35.866454+02:00 linux-5q3o kernel: [ 7680.344966] ACPI Error: AE_AML_PACKAGE_LIMIT, Index (0x000000008) is beyond end of object (length 0x8) (20181213/exoparg2-396)
2019-04-15T20:04:35.866499+02:00 linux-5q3o kernel: [ 7680.345167] ACPI Error: Method parse/execution failed \_SB.PCI0.LPCB.EC.BRNS, AE_AML_PACKAGE_LIMIT (20181213/psparse-531)
2019-04-15T20:04:35.866505+02:00 linux-5q3o kernel: [ 7680.345201] ACPI Error: Method parse/execution failed \_SB.PCI0.LPCB.EC._Q26, AE_AML_PACKAGE_LIMIT (20181213/psparse-531)


Is it possible that this is related to the problem that the internal battery is never used? Did not test this very intensely but my laptop will shutdown without warning after the first battery is empty.
The good part is that it first discharge BAT1 (the external battery)

Created attachment 282791 [details]
acpidump 1.21

Hello,

Updated to 1.21 and I think this is fixed

Or maybe not completely, the status of BAT0 always (AC plugged-in or not) shows "Unknown"

$ cat /sys/class/power_supply/BAT0/status
Unknown

BAT1 is showing the proper state Full/Discharging

Are you using firmware version N27ET35W?

Yes I'm using N27ET35W

Great, that was the change that Lenovo pushed to resolve the ACPI error. From what they said through email, the BAT0 status being unknown seems to be expected. This bug is about ACPI errors and they have been solved so I'll close this bug. If you feel that this BAT0's unknown status is bothersome, please file a separate bug.

I'm getting exactly the same errors with the last UEFI firmare from Lenovo (v1.58 released 04 Dec 2019): 
[   14.102849] thinkpad_acpi: ThinkPad ACPI Extras v0.26
[   14.102850] thinkpad_acpi: http://ibm-acpi.sf.net/
[   14.102850] thinkpad_acpi: ThinkPad BIOS N2IET80P (1.58 ), EC unknown
[   14.102851] thinkpad_acpi: Lenovo ThinkPad T490, model 20N2CTO1WW

Here is my dmesg:
déc. 08 20:48:33 hostname kernel: ACPI BIOS Error (bug): Could not resolve [\_SB.PCI0.RP09.PEGP.NVDN], AE_NOT_FOUND (20180810/psargs-330)
déc. 08 20:48:33 hostname kernel: ACPI Error: Method parse/execution failed \_SB.PCI0.LPCB.EC._Q27, AE_NOT_FOUND (20180810/psparse-514)
déc. 08 20:48:33 hostname root[1558]: AC adapter plugged/unplugged
déc. 08 20:48:35 hostname kernel: ACPI BIOS Error (bug): Could not resolve [\_SB.PCI0.RP09.PEGP.NVDN], AE_NOT_FOUND (20180810/psargs-330)
déc. 08 20:48:35 hostname kernel: ACPI Error: Method parse/execution failed \_SB.PCI0.LPCB.EC._Q26, AE_NOT_FOUND (20180810/psparse-514)
déc. 08 20:48:35 hostname root[1561]: AC adapter plugged/unplugged

(AC adapter messages comes from acpid)

Is a fix planned ?