Frequent laptop crash, what to do?

Hi, I've had a Medion laptop for a few years. However, this has recently had the problem that it suddenly crashes even when the battery is charged. There's no warning before or after, etc. When he's on the power cable, I've never had it, which is why I think it could be a kind of loose connection. Do you have any idea what that could be or how to fix it? LG

The battery is probably broken.

Yes, I thought at first, but I've already replaced it.

If the power supply to the motherboard through the battery has a loose connection or a defect. Then you can't do anything anymore.

OK thank you