• Please review our updated Terms and Rules here

Replacing my 486's CMOS battery

T

Tr3vor

Experienced Member
Joined
Feb 7, 2012
Messages
183
Location
Jerome, ID
So my 486 had one of those standard canister style batteries in it. It was removed when I got it so I spent the year having to enter all my settings in the BIOS every time I started it up. I'm getting bored of that.

So what can I use to replace that battery? I was thinking a AA holder type deal for the power but I don't know whether I need 2 or 4 batteries to keep this thing up. Also I've heard that those batteries charged themselves, so I'm wondering if I need a resistor or diode or something to stop that from happening.
 
If your motherboard has an external battery header you just plug the AA holder in there. Four is the usual replacement. You might need to change a jumper to access the external battery if your board has that as an option.
 
Another option is to replace the original NiCd barrel battery with a 3-cell (3.6V) portable (not cell) phone battery, usually around $2.00 at your local $ store.
 
I think the original owner had the same idea with the phone battery.
DLkdkYp.jpg


I might try that.

Ironically though the canister battery didn't leak on the board. That phone battery did or something. There is corrosion around the power supply and ram slots and not a spot of corrosion around the battery's solder location...
 
Tr3vor said:
I think the original owner had the same idea with the phone battery.

I might try that.

Ironically though the canister battery didn't leak on the board. That phone battery did or something. There is corrosion around the power supply and ram slots and not a spot of corrosion around the battery's solder location...
Click to expand...
Maybe I've just been lucky but I've never had any phone batteries leak (they're usually sealed); I certainly have had alkaline and NiCd AAs in battery holders leak; maybe that's what he had taped to the side of the power supply? The pins in that connector look too thick for a phone battery but right for an AA or AAA battery holder.
 
Was the original battery a lithium primary or a rechargeable NiCd? If the former, three AA batteries will work in a pinch; if the latter, the same goes, but add a MOSFET to avoid trying to charge the AA cells (less forward voltage drop than a diode).

What is your motherboard, anyway?
 
The motherboard is a PWA-IH4077C BD.
I couldn't find anything about it online.

Motherf*cker! Gosh dang I'm blind. I always knew what the battery header looked like. Its right next to the first ISA slot. I swear I looked over this board like 5 times for one... So that one would take 4 AAs right?
I officially feel completely stupid :\

There is an arrow on the header, which is positive and which is negative?
 
I was able to replace these batteries with a CR2032. You just need a holder and a diode (anything will do) to prevent the machine trying to charge the coin cell.
 
Don't worry about a blocking diode if you've got the 4-pin header. There's a bit of difference between makes as to pin assignments (e.g. on one board that I have the two inner pins 2,3 are jumpered to clear CMOS). Regardless, the power connections for the external battery are 1 and 4. Usually 1 is + and 4 is -, but check for continuity between pin 4 and the chassis before you plug your battery in. 6V (4xAA was the usual practice; my systems all use this, but 4.5V shouldn't hurt a thing either).
 
So Since I found that, I just soldered 3 batteries for 4.5v and stuck an FDD power cable to the end of the cord.

jNxEyyul.jpg
ToyYxS8l.jpg


I guess we'll see if this works.

Thanks for all the help
 
Stone said:
Because, it, too, *will* eventually leak. :) It's just a badly designed battery.
Click to expand...

Maybe somewhere down the line. However, if I were you, I wouldn't hold my breath. I've got some boards way over 20 years old and the batteries are still working. The trick is to keep an eye on your stuff and not let things rot in a corner somewhere. ;)
 
Agent Orange said:
Maybe somewhere down the line. However, if I were you, I wouldn't hold my breath. I've got some boards way over 20 years old and the batteries are still working. The trick is to keep an eye on your stuff and not let things rot in a corner somewhere. ;)
Click to expand...
I think 20 or 25 years qualifies as 'eventually'. :)
 
Stone said:
Because, it, too, *will* eventually leak. :) It's just a badly designed battery.
Click to expand...
Oh, I don't know...

I hate to agree with A.O., but I've also got 30+ year old systems here still with original barrel batteries like that and they still hold a charge and either show no leakage at all or just the first signs around the seal; in fact, I just picked one like that up yesterday, mfg'd June 83, that's been sitting in a closet for at least 10 years or so with an original battery just showing a little green on the - terminal. On the other hand I have no shortage of systems (sometimes the same ones) and devices that have suffered extensive damage caused by leaking NiCD, alkaline or carbon-zinc AAA/AA/C/D batteries, even mounted remotely off the board and connected with wires, which is what I suspect is the OP's situation.

I've got terminals where the entire power supply was effectively destroyed, with considerable damage also to the main board, all from two AA NiCds mounted off the board and connected with 3" leads; really amazing how that stuff can migrate along wires, traces and leads...

Not to say that I haven't had leakage from the barrels as well, but I think it's more a question of usage, current drain, charge level, age, make, etc. and not really a bad design.

Bottom line, as he said: Check them frequently, whatever type.
 
Last edited:
You must log in or register to reply here.
Back
Top