HP Omen 15 won't turn on if battery is installed and is not fully charged

Dear community,
I've tried every option and checked every page on Google but I am not able to solve this problem.

My girlfriend has a HP Omen 15 gaming laptop. It worked perfectly fine until one day, it won't turn on.
At home, I investigated the laptop and it seems like when I disconnect the battery and just power the laptop with the AC adapter, it will turn on.
(Before I can turn on the laptop without the battery, I have to hard reset the laptop by pressing power button 8 - 15 seconds without the AC adapter).
So I figured, dead battery.
Bought a new identical battery which just arrived yesterday and installed it with the same connector as the old battery.
It will still not turn on.
As soon as I disconnect the battery from the motherboard, and then hard reset the laptop and power it back on the AC power, it will turn on.

The only way the laptop will work WITH battery installed is the following way:

1. Disconnect battery (but make sure one end of the connector cable is connected to the motherboard)
2. Hard reset laptop (power button 8-15 seconds)
3. Power on laptop to the AC power
4. Turn ON laptop (Laptop boots!)
5. While the laptop is on, slam back in the other end of the connector in to the battery
6. The laptop is now ON with the battery and if you remove the AC adapter the laptop works on battery only

Now the laptop works perfectly fine with only battery, and with AC power.
You can turn it off, turn it on. No problems at all.
But now:
As soon as the laptop goes into Sleepmode, OR the battery drains to 0% and the laptop shut downs, we are back to where we started.
No way to boot up the laptop unless following the step guide described here above.

We need a permanent fix, because it is impossible to remove the case every time we need to disconnect and reconnect the battery. Unfortunately the warranty has expired.
As for now, I have left the battery out of the laptop, so the laptop only works on AC power.
Works most of the times, but sometimes still needs a hard reset in order to boot up the laptop on just AC power.

What we've tried:

• Updating BIOS to newest version
• Hard resets
• Updating Windows
• Updating Drivers
• Uninstall Battery drivers in Device Manager and reinstall
• Using HP Diagnostic app on Windows 10 to check battery
• Installing brand new battery
• Switching connector ends

We are desperately searching for an answer.
Hope anyone here can help us.

Thanks in advance!

 

Bump ~ Anyone with ideas?

 

Stop using sleep mode it can be problematic