Posting this here in case it helps anyone in the future.
I have a 93,000 mile, 2014 Octavia 1.4TSI estate. I've owned it since it was 9 months only. Until very recently, it was running on the original battery (assuming it hadn't been changed in the 9 months before I had it...)
The stop-start system had become quite sporadic in its operation. The display normally said "Power Consumption Too High". Then, seemingly completely unrelated, I started getting warnings about failures in the rear number plate bulbs. There was nothing wrong with the bulbs, and tapping the lights and/or opening/shutting the tailgate often "fixed" the problem - suggesting a dodgy connection somewhere.
The, one morning I got a "battery low warning" flash up on starting the vehicle. I completed a 45 min drive, left the car for ~4 hours, then drove back again 45 minutes. On locking the car, the mirrors did not fold in. I thus booked in for a new battery the next day. On trying to start it the next day, the battery was completely flat. I got it jump-started, and the battery replaced.
Since then, I have not had a single warning about the number plate bulb lights. They have worked flawlessly. Stop-start has also been far more available.
If you're still reading...
If your Octavia ever says "battery low" - it really means it. You may only have one start left before it dies...
Consistent "Power Consumption too High" messages explaining why stop-start is unavailable are a much better indicator of a failing battery in my experience.
I can only assume that I have a slightly high-resistance connection somewhere in the circuit to the number plate bulbs. If the overall system voltage was a little low before the battery change, would that explain why my error messages and non-working lights have now decided to fix themselves?