Thinkpad X220 crashes with battery?

I've had a Thinkpad X220 for a while. It was always reliable, but for about a week it occasionally crashes, but only with battery. It does not crash with BSOD, but with a strange picture and then restarts. Something does not happen on the charging cable. The error usually happens when lifting the laptop or heavier key presses. I would like to point out that I do not want to buy a new laptop, or (if possible) a new battery.

What could be the trigger?

In this case, there could be a bad contact point between the battery and the laptop in the cause.

Does the laptop really crash or is it off? If it is simply off, then clean the contacts of the battery and the remote station on the laptop and make sure that it sits properly.