problems after battery replacement

[Henk1959]

battery is replaced, after that a mwssage cmos reset 502 and a black screen. how can i fix this

[Hawks_Eye · Accepted solution]

Hi @Henk1959 

Welcome to the HP Support Community! We're here to help you get back up and running.

Thanks for sharing the situation—I'm really sorry you're facing this after replacing the battery. A CMOS Reset (502) message followed by a black screen typically means the system detected a BIOS configuration loss and is unable to proceed with normal startup. 

Let’s walk through a focused recovery path to bring your system back to life.

 

Step-by-step actions to resolve CMOS Reset 502 and black screen

1. Perform a full power reset
This clears residual charge and resets embedded controller states:

• Disconnect the power adapter
• If the battery is removable, take it out
• Press and hold the power button for 30 seconds
• Reconnect the battery and adapter
• Power on the system

2. Reset BIOS using key combination
If the screen remains black:

• With the laptop off, press and hold Win + B
• While holding those keys, press and hold the power button for 2–3 seconds, then release the power button but keep holding Win + B for another 10–15 seconds
• If successful, the system will beep or flash and attempt BIOS recovery
• Wait for the recovery screen to appear

3. Re-seat or recheck the CMOS battery (if accessible)
If you replaced a coin-cell CMOS battery:

• Power off and unplug the system
• Remove the CMOS battery for 5 minutes
• Reinsert it firmly and ensure polarity is correct
• Power on again

4. Attempt to enter BIOS manually
If the screen shows the CMOS Reset 502 message briefly:

• Press F10 repeatedly at startup to enter BIOS
• Once inside, go to Exit > Load Setup Defaults
• Save and exit

5. Reflash BIOS (if system remains unresponsive)
If the system doesn’t display anything:

• Use another PC to download the latest BIOS for your model from HP’s support site
• Create a BIOS recovery USB using the HP BIOS utility
• Insert the USB into the affected system
• Use the Win + B method again to trigger recovery

You can find the BIOS for your model here: HP Software and Driver Downloads

You're doing the right thing by addressing this early, and I’ll guide you through the next steps if needed.

If my response helped, please mark it as an Accepted Solution! ✅ It helps others and spreads support. 💙 Also, tapping "Yes" on "Was this reply helpful?" makes a big difference! Thanks! 😊

Take care, and have an amazing day!

Regards, 

Hawks_Eye

[Henk1959]

Meanwhile I found out the new battery had a failure so I had to return it for a new one. The steps you described were very helpfull in finding the cause. Now I have a good working laptop again.

Thanks!

[Hawks_Eye]

You are very welcome @Henk1959 

I’m glad to hear this story had a positive ending. The CMOS Reset 502 message and black screen can feel alarming, but your careful troubleshooting—combined with checking the replacement battery—helped isolate the real cause. It’s a great reminder that sometimes the simplest hardware issue, like a faulty new battery, can trigger complex‑looking errors.

The steps you followed (power reset, BIOS recovery attempts, reseating the CMOS battery) were exactly the right way to rule out configuration problems. Once you confirmed the battery itself was defective and replaced it, the system came back to life. That’s a textbook example of methodical troubleshooting leading to a clear resolution.

If you ever face similar issues again, the key points to remember are:

• Always start with a full power reset to clear residual charge.
• Use the Win + B BIOS recovery shortcut if the screen stays black.
• Double‑check new hardware components like batteries or memory modules when errors appear right after replacement.
• Keep the latest BIOS recovery tools handy from the HP Software and Driver Downloads page.

It’s great to know your laptop is working smoothly again. 

You're awesome, and I'm honored to have been your go-to guide! 😊

Stay fantastic, and have an amazing day ahead! 

Regards, 

Hawks_Eye

[Samrit26]

Hello,

What “CMOS Reset (502)” means on HP systems

CMOS 502 appears when:

• The RTC/CMOS lost power (very common after battery replacement)

• BIOS settings were reset to default

• The system detects an unexpected hardware state

On HP laptops, this is expected after:

• Main battery replacement

• RTC/coin-cell battery disconnect

• Power completely drained during service

So the error itself is not the failure — the black screen after it is the real issue.

---

Why you’re getting a black screen

After CMOS reset, HP systems may:

• Default to incorrect display output

• Fail POST due to incomplete power initialization

• Require manual BIOS reinitialization

This is not an OS issue yet — this is pre-boot.

---

Fix Process (Do this in order — don’t skip steps)

Step 1: Perform a full HP hard reset (critical)

This clears residual power and forces hardware re-detection.

1. Power off the laptop

2. Disconnect:

   • AC adapter

   • Main battery (if removable)

3. Press and hold Power button for 20–30 seconds

4. Reconnect AC adapter only

5. Do NOT reconnect external devices

6. Power on

➡️ If display comes back → proceed to Step 4
➡️ If still black → continue

---

Step 2: Force BIOS recovery (very important on HP)

HP systems can recover BIOS blindly even with black screen.

1. Power off

2. Press and hold:
   Windows key + B

3. While holding keys, press Power button for 2–3 seconds

4. Keep holding Win + B for 10–15 seconds

5. Release keys and wait (screen may stay black for 30–60 sec)

What to expect:

• Fans spin

• Caps Lock may blink

• BIOS recovery screen may appear

If BIOS screen appears → let it complete.

---

Step 3: External display check (to rule out panel issue)

CMOS reset can default to external output.

1. Connect HDMI monitor

2. Power on

3. Press F4 or Fn+F4 (display toggle) several times

If external display works → internal panel or cable issue.

---

Step 4: Enter BIOS and reconfigure (once display returns)

As soon as you see HP logo:

1. Press F10 (BIOS)

2. Load defaults:

   • F9 → Yes

3. Check:

   • System Time & Date

   • Boot Mode (UEFI)

4. Save with F10

This step prevents repeat CMOS errors.

---

If the screen NEVER comes back

At this point, one of these is likely:

• Battery replacement disturbed:

  • Display cable

  • RTC battery

  • Motherboard connector

• BIOS corruption

• System board damage

HP Support policy (important)

For hardware-level failure after battery service:
➡️ Only option is depot repair (ship to repair center)
There is no field fix once POST display is gone.

I do not recommend:

• Reflashing BIOS externally

• Random part swaps

• Continued power cycling