Battery drops "randomly" XPS 13 9380

Hi all,

I have noted an issue with my XPS 13 9380 (developer edition) for which I've been a very happy customer for now 3 years. I now noticed 3x the issue though without being able to see any similarity and the issue itself make it hard to spot when it starts.

Basically, laptop runs at full battery (100%) on AC and then starts charging from 93-94% (front led lights up as well) until 100% again. BIOS battery state says excellent, I ran the Dell firmware troubleshooting utility and it did not find any issues and the various BIOS logs do not register any issues. My battery capacity seems reasonable: 4637 mAh left out of 6842 mAh (about 70%). I never noticed any sudden drop or battery not holding charge and can still use it for several hours without being plugged in. The power profile in the BIOS was set to "adaptive" and never changed since I bought it.

The only 2 issues I ever noted on this laptop has been that from time to time (rarely) the wifi does not start, but that seems a known issue with the card & once or twice the Linux kernel shutdown the laptop after a cold boot detecting high thermal reading which seems to be a software bug that has not re-occured with the newest kernel.

Now, as to listing all that changed recently and may be related. I used to run Ubuntu LTS on it and switched to Fedora 36 recently, that means a newer Linux kernel (I hardly think this can be the reason though). I also had changed power strip (one grounded to one not grounded) but again I don't think that should make a difference. One last thing which should hardly matter, I've had to switch power cord (the cord before the transformer of the charger) to adapt from Swiss to European pins - it's rated for the same voltage, etc.

Perhaps more promising, the firmware went through several updates before the issue started to appear (though some weeks before). The firmware updater was broken on Ubuntu (not notifying me of new updates) and so the laptop went for about 2 years without BIOS update. I noticed it going through the logs and then applied updates. It went from BIOS 1.10 to 1.18 (and I subsequently updated to 1.19 and 1.20 "on time"). Of the versions between 1.10 and 1.18 I note the following that had to do with power or battery:

1.11: - Updated the Power Delivery firmware. - Updated the Thermal Algorithm.

1.12.1: - Updated the system Power Delivery firmware.

1.15: - Updated the default setting of Battery Charge Configuration in the BIOS from Adaptive to Primarily AC Use.

Lastly, I note that the battery, when full, has a small discharge current as seen from the OS (using tlp-stat, shows 1 mA discharge current) and from the diag tool, see photos (don't mind the 55% charge, I was changing the power profile to see if I could note any other issue and so it was set to only resume charging when reaching 50%, but so the laptop was on AC then, same data seen when the battery is at 100%). There the battery state change from idle to discharging (small current), back and forth.

I wonder if it could be either of the following:

• Battery malfunctioning? Maybe one cell reports being full without being full and then refreshes? Now I'm regularly checking the capacity but I'm not sure I would see anything and I don't know when the issue will trigger next, so it's a bit tedious.

• The default change from Adaptive to Primarily AC use in the BIOS messed things up (my default was still "Adaptive" after the BIOS update as I manually changed it to Primarily AC recently in between the 2nd and 3rd occurrence of the issue)

• Some BIOS bug?

One IT friend told me that some similar problem, for Lenovo, can be solved through the "reset hole" at the bottom of it "A Lenovo laptop with a built-in battery that won't turn on or wake up from a sleep state can be reset by pressing the pin-hole emergency reset" but Dell does not seem to have an equivalent and I would like to avoid resetting the BIOS as I've modified the bootloader significantly and that would probably mean a full re-install of my OS.

I called a support technician that said it could either be the charger, the battery, the charging port, the motherboard and advice to start with changing the charger. I did plugged the charger into one of the other USB-C port and registered the same micro battery losses. On this, he said that batteries should not loose power at all when on AC. I'm seeing conflicting info about this online but that would point to a charger/battery (motherboard?) issue as oppose to a firmware issue.

I think I've done all of the homework I could do apart from changing parts so would appreciate any thoughts before I buy some new charger and/or battery.

Many thanks in advance!

Tom