CMOS Battery removal / replacement

[peterbata]

Hello all. I was thinking of replacing the CMOS battery on my Z820. I noticed that if I unplug the machine and leave it unplugged for a day or two I have to readjust the time for example. And, very possibly other settings as well. I attempted to remove the battery a few days ago but stopped a few seconds in as I was getting a little squeamish. It just wasn't coming out as I thought that it should. Would anyone care to share their battery removal anectode with me. I would really appreciate it. Peter

[Paul_Tikkanen]

Hi:

Perhaps this video will be of help to you...

HP Z820 | REMOVE CMOS BATTERY TO RESET BIOS (FIX BOOT ERRORS) (youtube.com)

[peterbata]

Thank you for that link Paul. Much appreciated.

RE: The YT tutorial. Did you notice how you never actually see the battery pop out of it's socket in the video?. There is a quick edit then use see it lying on the motherboard. No matter. I will carefully attempt the removal again.

[SDH · Accepted solution]

Some added tips:

Obvious to many... but unplug from the wall and disconnect all peripherals first. I've seen power fed into the motherboard keeping a LED on it glowing from an attached DVI video cable attached to a monitor that was "turned off".

I get nervous seeing a small metal screwdriver used. I like to use a sharp-ended bamboo skewer stick used instead... not a tiny one but rather at least a 1/8" diameter one.  You want to do this the correct way because you can tear the battery holder off the motherboard if you don't. Google has info on that and repair methods.

You want to approach the battery if possible from opposite of the plastic "pocket" in the holder's edge (you can clearly see that in the video). You want to lift the edge of the battery opposite to the pocket so it slips up and out. In this case you'd want to approach the battery edge from above, and to remove the big video card and whatever else is necessary first to get a good angle on that upper edge of the battery. Maybe cut the skewer stick down in length to help with that.

Yes, I've seen a battery launched up and above of the case and back down inside. Not much of an issue if everything is not energized. Proper technique avoids this.

Clearing the CMOS... I've read press and hold for 30 seconds as the right method, and do that. Then over to the power-on button with press and hold same 30 seconds, and then back and forth a few times (all with the battery out and power supply disconnected from the mains). It takes a few repeats before the capacitors are discharged enough to finally have BIOS mention that date and time are not registering correctly. DGroves says that is the key signal that you've gotten to a full CMOS reset and are down to factory defaults.

[Paul_Tikkanen]

You're very welcome.

I use a smaller jeweler's screwdriver (the biggest size driver in those sets of five) to remove CMOS batteries.

That person's screwdriver blade seemed a bit too thick to me.

I have every confidence that you will be successful in removing the battery without breaking anything.

[peterbata]

Thank you for chiming in @SDH. Much appreciated as always.

There is no way that I was going to use a metal prod of any sort. I was thinking more along the lines of a wooden skewer. The type that my lovely wife uses when preparing kebabs. I would shorten it of course. What really concerned me was breaking those small plastic tabs opposite the larger plastic "pocket" as you so well put it. They seem fragile. Is clearing the CMOS something that is absolutely necerssary. Isn't changing the battery sufficient. Forgive me I'm just not seeing the connection.

[SDH]

It is an odd design but approaching from opposite the pocket seems to give just enough room to slip that top edge up and out. I'm guessing that a tiny screwdriver if carefully used from the same direction would work too... Paul has lots of experience and would know.

Pulling the battery out and putting it right back in is not enough. There are motherboard capacitors that hold a charge and thus can keep the BIOS settings stuck. Supercapacitors are even now being used as small batteries in some devices. CMOS data can get corrupted, and pushing the yellow reset button may not be enough. Just last week I had to use this deep CMOS reset method on a Z640 here to clear some weirdness in BIOS... I could not get to factory default BIOS settings the normal way. Once again it worked. It can't fix everything but is a good trick to know.

[peterbata]

Understood @SDH. Slow and steady is how I plan on plotting forward. I think that I will start off with a small wooden pry bar first. Thanks again for your help. That goes for everyone.

[SDH]

Peter,

Got some pics from a dead Z640 motherboard for you. It turns out that exactly opposite from the battery socket's "pocket" area is a roughly 2mm wide vertical slot built into the plastic. If you look at the pic below it is clear that is where your bamboo skewer is supposed to go to lift up on that edge of the battery. There are two upper edge thin rims of plastic, one on each side of the slot, so you have to push the battery edge a bit towards the pocket to get it free from being under those rims. Knowing about the vertical slot is key... Paul's mini-screwdriver would fit in there perfectly.

I wish HP had rotated the socket so there was easier access to that slot. Attached also is a pic of a pik I tried... it gets under the battery but does not allow pushing towards the pocket where springy contacts are for this purpose.  I think your skewer will let you get in the slot, under the battery edge and let you pry towards the pocket all at once.    😊

Pocket, slot and 2 rims

Pic of a pik...

[peterbata]

Wonderful. Thanks so much for taking the time to provide me with those photos. That will defintely help.

"There are two upper edge thin rims of plastic, one on each side of the slot" Those are exactly the two plastic edges that protrude from the side of the socket. I was terrified of cracking either one of them when trying to lift the battery out from the socket. Inserting the small bamboo pick in between those two small tabs is probably going to be my safest bet