CMOS Checksum Error after hardware upgrade

[SNico1]

Hi everyone,

My Laptop Model: hp 15-dw3757ng

OS: Windows 11

I recently replaced the laptop battery and upgraded my SSD from 1TB to 2TB. After turning on it shows the famous '502 CMOS Checksum invalid' error. Right after the automatic restart, my laptop is showing a black screen (with backlight turned on and fan running). Apart from that, nothing happens.

What I did for replacement:

1. Cloned OLD standard SSD with Acronis True Image (and auto settings) to NEW SSD (Crucial P310)

2. Turned off laptop, disconnected charger

3. Took out old battery

4. Took out old SSD, replaced with new SSD

5. Replaced battery with new one

I already read through some suggestions, nothing helped so far. 

- Resetting BIOS to default settings doesn't change the behaviour

- Windows + V will bring back the 502 error

- Windows + B and Update brought 500 error

- Esc -> f2 to run diagnostics: All checks fine

- Plugging in the OLD SSD via USB and selecting as first boot option brings the same behaviour as with new SSD 

Please find some pictures attached.

Thanks for your support!

 

[Kuroi_Kenshi]

Hi @SNico1,

Welcome to the HP Support Community!

Thanks for reaching out!

We're thrilled to have the opportunity to assist you and provide a solution.

I understand your HP 15-dw3757ng is showing a 502 CMOS Checksum Invalid error after replacing the battery and upgrading the SSD, and now gets stuck on a black screen after the automatic restart. Let’s go through a few steps to isolate whether this is a BIOS/CMOS issue, a bootloader issue, or a hardware seating problem.

Do a full CMOS reset (hard reset of NVRAM)
– Disconnect the charger.
– Remove the back cover again, disconnect the main battery and also unplug the small CMOS coin-cell cable if your model has one.
– Hold the power button for 20 seconds, reconnect both batteries, then try booting again.

Boot once without the SSD installed
– Remove the SSD and power on with only the battery connected.
– If the BIOS loads or shows “No Boot Device,” it confirms the SSD or bootloader is causing the freeze.

Reseat the new SSD carefully
– Remove the SSD, reinsert it fully, and tighten the screw.
– Make sure the SSD is NVMe and compatible with the PCIe slot (this model sometimes has issues with certain Gen4 SSDs and runs best on PCIe Gen3).

Clear potential BIOS corruption
– Start the laptop and hold Windows + V again for 10–15 seconds.
– If prompted, choose to apply the BIOS update/reset.
– If the BIOS tries to repair and restarts, let it complete fully before pressing any keys.

Try entering BIOS without any bootable media
– Power on → immediately tap Esc repeatedly.
– If the Startup Menu loads consistently with the SSD removed but not with it inserted, the new SSD firmware or cloning process may be the cause.

Test with the old SSD inside the laptop (not USB)
– Insert the old SSD back into the internal slot.
– If the system still gives a checksum error and black screen, the issue is unrelated to the drive and likely due to CMOS/NVRAM corruption from the battery swap.

Rebuild the bootloader on the new SSD (if BIOS loads normally)
– If you manage to boot into HP UEFI or Windows Recovery:
– Go to Advanced Options → Command Prompt.
– Run “Automatic Repair” or rebuild the EFI partition using Windows recovery tools.
– Cloning tools sometimes create bad EFI entries that freeze HP BIOS during post-checksum reset.

Try powering on with AC only (battery removed)
– Remove the main battery, leave the SSD inserted, plug in the charger, and turn on.
– If the BIOS loads normally, the new battery may not be sending stable CMOS/RTC values on first initialization.

Update BIOS once the system boots
– If you get it to boot even once, update the BIOS to the latest version using HP Image Assistant or HP Support Assistant.

I hope this helps.

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