Undetected Battery / Laptop won't turn on unless it's plugged in

The battery is undetected but sometimes it detects for 2-3 seconds and switches back to undetected on Windows. On BIOS, the battery is undetected as well (doesn't show any SN). When charging the laptop, the light near the power jack switches between white and orange. The battery seems working fine, except for the fact that I can't turn it on without plugging the power brick first. When I try to power it on without power brick, it only shows 3 blinking white lights. Once it's on, I can safely remove the power brick and it can run fine on battery like normal but still undetected. When I hover on the battery icon on taskbar it shows '255% available' and 'plugged in' (even though it isn't).

Things I've tried so far

• Hard reset (removing battery/power and holding power button for 30 sec)
• Bought a new replacement battery (2x)
• Bought a new power brick
• Reinstalling the operating system (Windows, Linux, Cloudready) all same results
• Used HP assistant to check the battery status but it's undetected
• Updated BIOS

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The HP laptop in question is an HP Pavilion G6-1313EL and out of warranty. Normally, I would just buy a new laptop but this one is a gift from my son who recently passed away.