Laptop samsung 700z3a runs out of battery too soon despite high capacity

I have an old laptop samsung 700z3a from approximately 2012. It runs out of battery within 2-2.5 hours without heavy load. However, the battery is alive according to Power Manager: pic which shows that battery's capacity is at 86% of the designed one . The OS was Windows 7, I then replaced it with Debian 11, but the problem remains. Any idea what could be causing this? Or is it natural for this laptop? Given: Model: Samsung 700Z3A laptop OS: Debian 11 Capacity: 56 Wh (designed: 65 Wh) It works until it reaches 3%, then shuts down. So I guess that's another confirmation that the battery is fine

Question by WhiteBlackGoose on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.