Why does my laptop start up automatically after shutting down?

I've been desperate with my laptop for a few days…

After inserting a new battery, my laptop keeps going up by itself while drawing power from the battery after I shut it down. However, if the laptop is connected to the power supply and I shut it down, it stays off, but I can no longer boot it up using the power button (which was easily possible with the old battery).

This is my mother's four year old "Dell Latitude E5550" business laptop, where I decided to replace the broken battery, because otherwise I could only use the laptop with the power plug. The new battery is from Patona and has the same wattage, ampere and volt number as the new one.

How the laptop behaved at the time when the old battery was still working, I can't say, but I know that my mother never had problems with the device.

I have already tried the following and unfortunately made no change:

in the system controls under "Start and restore" the check for "automatically restart" removed in the event of a system error
disable the quick start of the laptop in the system controls
All applications deactivated in the Task Manager under "Autostart"
in the command prompt as administrator "sfc / scannow"

It would be great if any of you can help me solve this problem. I have been looking for a solution on the Internet for days, but all the tips that I was able to apply based on my skills were either inappropriate or did not help. I tried to enter the BIOS when the system started, but my "ESC" and "F1" attempts also failed (maybe I wasn't fast enough or pressed at the wrong time). I also read that you need a password for the BIOS (e.g. For resetting), which I don't have.

So: it would be great if someone could help me and I thank you in advance for answers!

I would say your power button just has a grain of sand somewhere

Is it soaked a bit? So it no longer clicks when you press it

Thank you for your answer! To your question: No, not at all, when the old battery was still in the laptop, I was able to start up the laptop easily using the power button.

May have changed in the meantime.