HP 255 G8 Notebook PC (2M9P0EA) battery issue

[SuhajdaFerenc]

Dear Members, Dear Experts,

In the following case, I ask for your help. About 2 months ago we sold a laptop: HP 255 G8 Notebook PC (2M9P0EA). About 2-3 weeks after the sale, the buyer called me: the laptop was stored OFF - NOT ASLEEP and after a few days the battery drain level was 14%. So: the battery drained from 100% to 86% when turned off. The battery has been replaced at the Hungarian service. Our client got the laptop back, called again after about 2 weeks: the battery continues to drain when the laptop is turned off. 9-12% can be established.
I reported to Customer Service in Hungary that the laptop is still discharged when turned off. In the laptop, the motherboard was replaced by service. The process was repeated: after replacing the motherboard, our client called me that the laptop was turned off, still draining 10-12% in a couple of days.
Yesterday I called Customer Service in Hungary, where I received an answer from the operator: they do not accept my warranty claim several times, the phenomenon is completely natural and normal, there is accurate documentation from HP. Although the operator couldn't find it anywhere for this type, he ended our conversation by saying that it is typical and acceptable for all types (?!). My question is, if our Client (and me) understands and unacceptable this answer, what else can I do?
Thank you all for your attention and help.

Have a nice day everyone,
Frank from Laptop.hu Ltd.

[BeemerBiker]

The laptop was either not actually shut down or had devices that consume power.  It is possible that WIndows 11 updates installed drivers that allow devices to consume power even when turned off.

Run the following command from the windows administrators command prompt

powercfg -devicequery wake_armed

for example the following devices are enabled even if the PC is turned off

They are all drawing power EVEN WHEN LAPTOP IS TURNED OFF.

(The above is not a 255 G8 as I do not have one)

You can disable these devices using the device manager as explained in step 1 here

Possibly the laptop was not properly turned off.  If the power button was pressed it is likely the laptop went to sleep instead.

You can look a the power plan and you can look at the sleep history to find if it was sleeping

Laptops have more power options than desktops.
There are battery reports and usage graphics.
You can defined what happens when you close the lid.
The power button can be used to cause the system to sleep
or the sleep button can cause hibernation. Here is a typical plan

You can examine the sleep history going back several days to determine if  it was sleeping 

Copy and paste the followind commands into the same window to get sleep history

powercfg /SleepStudy
.\SleepStudy-report.html