Battery lamp stays on after starting

If I don’t, the consumers will become weaker over time. I changed the voltage regulator on the alternator half a year ago. The V-belt on the alternator is also well tensed and the same is stuck. Does anyone have any idea what this can be about? Do the days still have to measure the alternator, but since they give after gas wall-mounted It doesn’t necessarily sound like it, does it? Thank you for your help. Greetings Bany