XPS-12 9Q33 Power Button unresponsive in sleep mode after (failed?) BIOS Update to A10

HI All, 

While using the Dell "SupportAssist" utility (in an attempt to diagnose an issue with the sound device) I saw that SupportAssist was strongly recommending that I update the system BIOS to version A10 to fix the latest Intel CPU vulnerability. Therefore, after closing all programs as suggested, I clicked on the appropriate link(s) to update the BIOS from there. The process started, proceeded for a few minutes, looked as if it had finished "verifying" the BIOS update, then appeared to hang when the Intel Firmware Update Utility started to run an a command window. Nevertheless, I left it alone overnight hoping it would sort itself out.

Unfortunately, the next day it didn't seem any better, but I noticed that an unrelated email notification had popped up on the screen, indicating that the OS was functioning, even though all the hardware inputs - even including the power button -  appeared to be disabled. I therefore connected remotely via Team Viewer and was able to restart the machine.

At that point, it seemed to be OK and I breathed a sigh of relief. MSINFO32 reported that the BIOS was updated to A10 as expected and the original issue with the sound device was also 'magically' fixed! I used it all day with no apparent problems and put it into sleep mode before I went to bed.

However, the next day, it seemed dead as a dodo! No response to anything, including the Power Button (even the 30 second 'trick' to force a hard reset). At that point I gave up, thinking that the BIOS update had bricked the machine. I unplugged it and left it to allow the battery to drain.

But then, the following day, I suddenly heard the fan working and then some notification sounds. The battery level was very low (7%) but it was working! I plugged it in again and it seemed fine. It appears that the low battery had triggered the "Reserve battery level" which wakes the machine from sleep! 

So now I have a machine that I daren't let go to sleep unless I want to risk it not turning on again. Dell support say that as it's out of warranty I need to pay for support to "talk me through" all possible scenarios, which I know is going to take ages, cost a lot of money and be unlikely to fix anything! A guy from Dell hardware support suggested that I should re-flash the BIOS and hope it works properly next time. Obviously, I'm very reluctant to do that in case it properly bricks the machine next time. At the moment the machine is at least working - sort of! - and I need it for work! 

Any thoughts, suggestions? Is there a way to ensure that the BIOS update succeeds if I decide to go down that path? 

Cheers
Steve