HP Spectre x360 15-bl000na no longer achieving 100% charge when plugged in and charging

[under_a_cloud]

My Spectre x360 15-bl000na is no longer achieving 100% charge when plugged in and charging.

Using the original power lead/cable, when I plug it in to charge the laptop, the battery charges up until 99% when I am using it but goes no further to reach 100%. However, when I am not using the laptop and it is plugged in and charging, the laptop charged to 100% and the red/amber light changes to the fully charged white light.

I have done all battery tests and it says everything is all OK but is it? Or is this some sort of weird Windows 10 error?

[Huffer]

Run the HP battery diagnostic test in the HP Support Assistant or in the UEFI preboot environment and report to us the advanced results so we can see all the data on the health of the battery, please. 

[under_a_cloud]

I have just done as suggested (this is after a charge, it is unplugged) and these are the results:

Warranty Type: 3

Cycle count: 228 / 1000

Manufacturer: 333-2C-10-A

Battery Age: 477 days

Temperature: 28 °C

Design Capacity: 6860 mAh

Full Charge Capacity: 6144 mAh (89%)

Remaining Capacity: 5053 mAh

Current: -2089 mA

Terminal Voltage: 11703 mV

Design Voltage: 11550 mV

Cell Voltage 1: 3897 mV

Cell Voltage 2: 3891 mV

Cell Voltage 3: 3892 mV

Cell Voltage 4: 0 mV

Status: C0

AC Power: No

CT Number: 6FZER06TZDT030

Adaptive Battery Optimizer: Not supported

[Huffer]

The battery is older but those results do not suggest it is bad. Still, I think the problem would be solved by replacing the battery. You would need to do so soon anyway.