Laptop uses an unusual amount of electricity?

I recently bought an used Acer v15 Nitro 593g laptop.

Everything was great, only I noticed that the battery is drained extremely quickly. According to several tests, he should persevere with light office work over 5 hours without problems. I took the laptop to a lecture, duration 90 minutes.

At the beginning the battery level was 96%, at the end of the lecture only 28%. I only programmed, so basically only edited text and occasionally carried out 2D tests, nothing that would be demanding on the hardware. I was in energy saving mode all the time.

So I thought the battery was just old (previous owner had had it for 2.8 years) and would have lost a lot of capacity. I let Windows issue the battery report and lo and behold: this is not the problem. The battery still has ~ 65 of the original 70Wh capacity.

The laptop should consume a maximum of 16W in office use. So arithmetically there should still be a runtime of 4h, and with the average of ~ 10W even more.

So why is it that the laptop uses so much more / the battery does so much less than would be deduced from the capacity?

With Task Manager let's see if a program is heavily loaded on the processor.

No, the processor is never more than 20% full.

If the battery is no longer displayed at full capacity after charging, then it has been exhausted. Windows continues to use the values of a new battery to calculate the runtime, of course, the results are then incorrect.

How did you set the display? If it is set very bright, then it needs a lot of electricity.

It was set to medium brightness, as in the tests