Laptop does not power on without charger even though battery shows 100% charged

[AroojSaleem-995]

I am using an HP EliteBook 820 G3. My laptop does not power on unless the charger is connected, even when the battery is fully charged (100%).

When I turn it on, I get the following POST error message:
"Real-Time Clock Power Loss (005)" and "The system time is invalid. This may be a result of a loss in battery power."

After this, the laptop only boots if the charger is plugged in. If I remove the charger, the laptop immediately shuts down.

I already checked the Windows battery report. The design capacity and full charge capacity both show 12,449 mWh, which seems very low compared to normal laptop batteries.

I think either the main battery is degraded or the CMOS/RTC battery is dead. Could you please confirm if replacing the CMOS battery and/or the main battery (SN03XL, 44Wh) will solve the problem?

[TheHelper0007]

Welcome to HP Support Community, @AroojSaleem-995.
 
Thank you for posting your query, I will be glad to help you.

Based on the symptoms you've described, it appears you're facing two distinct hardware issues simultaneously: a failed main battery and a dead CMOS battery.

Here’s a breakdown of the problems and how to solve them.

Problem 1: Immediate Shutdown When Unplugged (Main Battery Issue)

While the symptoms (immediate shutdown and a very low capacity of 12,449 mWh in the battery report) strongly indicate the main battery has failed, running a hardware diagnostic test will give you a definitive confirmation.

Action: Run the HP Battery Test.

1. Shut down the laptop completely. Make sure the AC adapter is plugged in.
2. Press the power button and immediately start tapping the Esc key repeatedly (about once every second) until the Startup Menu appears.
3. From the Startup Menu, press the F2 key to enter HP PC Hardware Diagnostics.
4. In the diagnostics menu, select Component Tests.
5. From the list of components, select Power.
6. Select Battery, and then click Run once.
7. The test will start. It usually takes a few minutes.
8. If the test FAILS: It will provide a "Failure ID" code. This is your confirmation that the battery is faulty and you will need to replace it.
9. If the test passes, try calibrating the battery.

Problem 2: "Real-Time Clock Power Loss (005)" Error
This error is separate from the main battery issue. Here are the steps to resolve it.

1. Update the BIOS: Visit the official HP support website for your EliteBook 820 G3 and install any available BIOS updates, as this can sometimes fix hardware communication errors.
2. Remove and Reinstall the Real-Time Clock in Safe Mode: This process reinstalls the clock's driver. CAUTION: Only perform this in Safe Mode to avoid system damage.
   1. Restart in Safe Mode. (Hold Shift while clicking Restart from the sign-in screen, then navigate to Troubleshoot > Advanced options > Startup Settings > Restart and press F4).
   2. Once in Safe Mode, open Device Manager.
   3. Expand the System Devices category.
   4. Right-click System CMOS/real time clock, select Uninstall, and confirm.
   5. When prompted, click Yes to restart the computer. The driver will reinstall automatically.

I have attached the article for your reference.

3. Replace the CMOS/RTC Battery
If the error persists after the software fixes, the physical CMOS battery on the motherboard has failed and needs to be replaced. 

 
I hope this helps.
 
Take care and have a good day.