Thanks so much for the figure. As I understand, if I turned ZBx2 off for 2 years while keeping the AC power plugged in and limiting the max battery level to 80% in BIOS, then the charge and discharge bandwidth should be small enough, maybe always varying between 60% to 80%.
On the other hand, I got the following screenshots when running some tools:
These screenshots are taken after booting into Windows 10 on HDD in USB enclosure and leaving it charging for more than 3~5 hours. So it seems that the AC power charging during the recent 2 years never worked and the battery simply failed to get charged?? (I can confirm this, because when I unplugged the AC power plug from ZBx2, it immediately turned off) On the other hand, I’ve noticed that in ZBx2 BIOS, there is a “Fast Charge” setting in the “System Options Menu”, and the explanation (according to official document) is "When checked, battery charge rate is actively managed by the system using current battery and charger parameters. When unchecked, rate is fixed. " I always leave it as checked/enabled, so maybe this is the reason why it never got charged??
As a side note and comparison, here is the battery info of my >7 years old ThinkPad W540:
