Massive Battery Drain Overnight With Windows Shut Down

I've had this issue a few times, but the latest one was the impetus to post here.

About 95% of the time, I run the laptop on battery power only. If I'm using Davince Resolve, I'll run from the mains, but that only accounts for about 0.5% of the time. I fully charge it when it drops below the 20% mark, so that would account for the other 4.5%, as I'll be using it at the time, and want to finish what I'm doing.

Yesterday morning, I switched on the laptop, and was immediately greeted with the message to charge the battery. The battery level was showing 0%. The previous day, I had powered down the laptop at 14:52 and it was showing at 26%. This is what Windows shows.

Another curious one is the graph is for the 'Last 24 hours', yet the 'Screen on' value is over 21 hours! This is despite me shutting the laptop down at around 3:00pm.

I also ran the battery report, and this the excerpt from that for the same day. As you can see, when the laptop is initially switched on, the battery level was 22% (so a 4% loss overnight), and by the time it displayed the message, and I switched on the power supply (at arms length from me), the battery level was showing '-'.

I used HWinFO and it shows the battery having 0% wear level and a cycle count of 60, although I don't understand that one. I might switch the laptop on 3-4 times a day at most, and always power it down, so if the cycle count was every time the laptop was powered down, I could have reached that in less than a month, and yet I've had the laptop for over 2.5 years.

Fast Startup is also disabled.

So is Windows 'shut down' not shutting down completely? If not, is there a way to make it shut down fully.