If it is a used system, there is no telling what condition the battery is in. You can open an administrative command prompt and type powercfg /batteryreport and it will give you some info.
Since the 9365 is a Modern Standby system, it will use some power while the system is in low power mode. If you want to see that report, type powercfg /sleepstudy
Keep track of where each report is placed so you can copy it to the desktop to read, if necessary.
You might also run the command below just to see if the system is still in its original configuration or has been modified.
There are other reports, just type powercfg /?
I will compare my two year old system with your reports but my system has not had heavy usage.
I don't remember my system dropping that far that fast. But it may be a problem of the info on the battery being updated to show the new number.
You say the battery was at 100% and was drained to 60% and then dropped to 4% quickly. What were you doing and how long did it take to go from 100% to 60%?
1. Could you please update the "Microsoft ACPI-Compliant Control Method Battery"?
Our other customers met the same problem, but it was resolved after updating the Microsoft ACPI-Compliant Control Method Battery.
2. update your BOIS, Check this link to get steps https://www.dell.com/support/article/cn/zh/cndhs1/sln304833/xps-13-9365-2-in-1-why-the-battery-drain...
3. If you can not resolve your problem from above two steps ,then try to get a new XPS 9365 2 in 1 battery HMPFH 7.6V, 5940mAh