CMOS is invalid. Error 502. Computer shuts down when power supply is removed.

[SimonD10]

My HP Pavillion Gaming Laptop 15-cx0xxx recently started having complications starting up. 

It began showing the 502 error while trying to reboot which it struggled a lot with. Removing my battery helped to start it up again, but it still gives the same error every time I want to start it up. 

Furthermore, my PC shuts down immediately when the power supply is removed, which could indicate that the battery is dead, even though I changed it a year ago. (It shows fully charged btw)

I have tried almost everything except resetting my pc to fabric setting (which I don't believe will work) or tried a new battery. 

What do you think I should do? 

Thanks in advance,

from a frustrated engineering student... 

[Garp_senchau]

Hi @SimonD10, 

Welcome to HP Support Community!

We noticed that this thread hasn't had any updates in a while since your original post; while this is rare, we didn't want this post to remain unanswered, so, here's the solution to your query. We hope it helps you and everyone viewing this post 😊

Replace the CMOS Battery

• This is a small coin-cell battery on the motherboard.

• Symptoms of a dead CMOS battery: 502 error, BIOS resets, clock resets.

• Very inexpensive to replace and often resolves BIOS boot issues.

Test with Another Battery (if possible)

• Borrow or buy a known good replacement battery.

• If the system still dies when unplugged, the problem might be on the motherboard (charging circuit).

BIOS Reset & Update

• Enter BIOS during boot (Esc or F10 on HPs).

• Restore defaults and save changes.

• Optionally, download the latest BIOS from HP’s official site and update it using their tool.

Run HP Hardware Diagnostics

• Press Esc during boot, then F2 to enter diagnostics.

• Run battery and system tests — this might help confirm battery or motherboard faults.

Please mark this post as “Accepted Solution” if the issue is resolved, and if you feel this reply was helpful, click “Yes”.

Thanks for being part of the HP Community!

Regards,