Part of what is making it confusing is that you are fairly new to lithium ion lights.
Most lithium ion lights that have turbo will not access turbo once the battery voltage gets down to around 3.7 volts.
So when you realize you can’t access turbo it is time to charge the battery.
The manual specifies that the Amber battery indicator flashing every 4 seconds is 25% of battery but that is really oversimplifying things. The light will go from green to Amber a lot sooner when you are on one of the turbo modes versus one of the lower medium modes or Firefly. This has to do with voltage drop at higher modes. When I see the light goes to Amber when I’m on the first turbo, it’s time to charge the battery. It doesn’t have to be done immediately right then and there but at the end of the day it is getting charged.
The other thing that’s making this confusing is reading the general UI instructions and the advanced UI instructions. The advanced UI is so much better for so many reasons that you should just forget about the general UI.