Based on the data you provided, I can reassure you that your YUKA 1000 is performing well.

Here is a breakdown of why this is normal and what to expect:

1. The Math
You covered 280 m² and used 77% of your battery (dropping from 100% to 23%).

This means your mower is on track to cover approximately 360 m² on a single full charge.
For a YUKA 1000, Mammotion generally estimates a mowing capacity of around 200 m² to 350 m² per charge, depending on the grass conditions and lawn complexity.

Since you managed to do 280 m² and still had nearly a quarter of the battery left, your mower is actually performing at the higher end of its expected efficiency.

2. Factors That Influence Battery Drain
If you feel the battery is draining faster than you expected, it is likely due to one of these "real-world" factors:

Grass Height: If the grass was a bit long or thick (which is common for the first few mows of the season), the cutting motor has to work much harder, which draws more current from the battery.

Complexity: If your lawn has lots of turns, obstacles, or a complex shape, the drive motors use more energy for maneuvering compared to long, straight runs.

Slopes: Even a "gentle slope" requires more power to climb than a perfectly flat lawn.

Overlap Settings: If you have a high "path overlap" set in the app (meaning the mower overlaps its previous path significantly to ensure no strips are left), it travels a further distance to cover the same square footage.

3. Why 23% is the "Sweet Spot"
Robotic mowers are designed to head back to the charging station when they hit around 15%–20% battery. This is a safety margin to ensure they have enough power to navigate back to the dock, especially if they have to travel across a large lawn or through a narrow path.

Summary
You do not have a battery problem. Covering 280 m² and finishing with 23% remaining is a very healthy result. As the mower begins to maintain the lawn regularly (cutting only a few millimeters of grass at a time), you may even see the efficiency improve slightly because the motor won't have to work as hard to spin the blades.