Inspiron 7380, battery issues, #2

I have an Inspiron 13 7380 running Windows 10 Home, purchased in April 2019.

A couple of months ago, I had to replace the original battery as it was swollen. The new battery has performed flawlessly.

The only other maintenance I've had to perform is fan replacement.

This week, the laptop suddenly crashed and then switched off, whilst on mains power (the battery was also fully charged). After checking a few things, it appeared that a faulty WD external USB drive was getting warm, and presumably caused some protection to kick in.

Removing the external drive was just the start of the problem though. The machine would no longer work on battery. I thought the machine was confused, so disconnected the battery, held down the power button for 60 seconds, then reconnected and restarted.

After that, the machine wouldn't let me log in unless I entered the BitLocker recovery code - every time.

Event Viewer log showed

"Bootmgr failed to obtain the BitLocker volume master key from the TPM. 24636"

I got tired of entering the Bitlocker code, so I decide to temporarily disable it by switching off disk encryption in Windows - it took all night to decrypt, but it was one less thing to contend with.

At this point, the machine was also failing to remember my login PIN, and wouldn't let me use my fingerprint - I had to use the administrator password.

All Dell software, firmware and BIOS updates are installed, as are all Windows 10 (may 2020 version).

The machine is now working perfectly, EXCEPT that it doesn't seem to know the correct level of battery charge.

If I use the machine on battery, the level suddenly drops from 100% to 6%, gives a critical warning then shuts down. Conversely, when I switch it back on with the charger plugged in, it will say something 4 hours to full charge, then suddenly shoot up from 7% to 100%.

Regarding the TPM message I got, there is no TPM setting in the BIOS, only PTT. Windows was reporting that the TPM service wasn't running. I've set PTT to enabled, and Windows is now reporting TPM on, but I thought they were slightly different things ?

I'm not sure what to do next, so any suggestions appreciated.

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