How to fix “CMOS Checksum is Invalid (Error 502)” on HP Notebook - 15-da0299tu

[Ak23_]

Hi,

My laptop shuts down by itself, and sometimes it does not turn back on unless I connect the charger. When it finally turns on, it shows this message:

"CMOS Checksum is Invalid (Error 502)."

I don’t know why this message is showing or what the problem is. Please tell me how to fix this and what I need to change or check.

Thank you.

I would really appreciate step-by-step guidance.

[Deep_World]

Hi @Ak23_,

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’m sorry you’re going through this; I understand the concern and don’t worry I’ll help you with this.

To better understand the issue, could you please provide a few more details?

1. How old is your laptop, and was it recently updated or repaired?
2. Does the laptop show the CMOS error every time you turn it on, or only after a full shutdown?
3. Is this the original battery and charger, or have they been replaced before?

From your description, this sounds like a CMOS/battery-related issue, likely tied to your laptop’s internal CMOS (BIOS) battery. This battery keeps BIOS settings stored when the laptop is powered off. A failing CMOS battery can cause the “Checksum Invalid” error and may also make the laptop unable to start without being plugged in.

Here are some steps you can try:

1. Reset BIOS settings:
   • Turn off the laptop and remove the charger.
   • Press the power button for 15–30 seconds to drain residual power.
   • Plug in the charger and boot into BIOS (usually pressing F10 or Esc on HP laptops).
   • Choose Load Setup Defaults or Reset BIOS to Default, save, and exit.
      
2. Update BIOS:
   • If the CMOS battery replacement doesn’t fully resolve it, updating the BIOS via HP’s official website can sometimes help.

I hope this helps 

I'm glad I could help! 😊 If this resolved your issue, please mark it as "Accepted Solution" and click "Yes" on "Was this reply helpful?" Your feedback not only keeps us going but also helps others find the solution faster! 

Take care and have an amazing day ahead! 

Best regards,

Deep_World

[Ak23_]

Hi, thank you for your follow-up.

My laptop is from 2018, and it has been upgraded to Windows 11.

The CMOS error does not appear every time. It only happens when the battery level drops below around 40%. At that point, the laptop shuts down by itself and then does not turn on until I plug in the charger. After connecting the charger and turning it on, the “CMOS Checksum is Invalid (Error 502)” message appears.

I replaced the original battery in December 2024 with a Techie Laptop Battery for HP HT03XL – 3400mAh (3-cell). The charger is original.

Please advise what I should do next and how to fix this permanently.
Thank you.