So I ordered a replacement battery from a big eBay seller branded #CameronSino, as I could not find a genuine one anywhere.
But after the laptop is in my bag for some hours, I can turn on the laptop but there is no left capacity reportet. After reinstalling the battery, everything will be fine.
Anybody has an idea which manufacturer to chose? #Lenovo #Thinkpad #P71
Battery does not drain, also I always shut down properly. Still I will double check next time.