What's wrong with the battery?

Question

Batteries

For 2.5 years of active use, the battery capacity has decreased and does not last more than 20 minutes without being connected to the network.
It doesn't seem to bother me much, and the reasons are clear.
But now the following has begun:
the network connection spontaneously turns off and on every 30-40 seconds, i.e. Charger is plugged in but not charging.
If you remove the battery, the laptop works fine from the mains.
What could it possibly be?

Answer 1

The controller on the battery dies, this is relatively normal. May interfere with touchpad/keyboard in some cases

Answer 2

Or the battery, or the charger, dies further. It happens - over time, the charger does not have enough strength to charge the battery while the laptop is running.
Try with a different charger.