Set the wayback machine for this one (CMOS Battery)

tincanalley · July 28, 2019

I dragged out my old machine from '95 to clean it up and make it my DOS and W98 gaming machine. During the disassembling process to clean it and streamline the components I noticed the CMOS battery was leaking. It is a 3.6V NIMH and soldered to the board. I ordered a replacement, but then noticed near the battery is a 4 pin external battery connection. I determined only pin 1 and 4 are used, but that's all I could find out. I didn't find a way to switch to that connection, nor if it also has to be a rechargeable NIMH. So, here's my question... Do I need to desolder the old battery to use the external connection? Does the battery connected to the pins need to be a rechargeable or can I use a lithium battery?

Oh, on a side question... The board has a USB 1.0 header that's only 8 pins. From what I can find, the pinouts are the same as USB 2.0, so I think a normal rear panel USB designed for 2.0 should work. Just not sure if I can get W98SE to use it. Any thoughts? It's not really a huge issue as it won't be needed for gaming. Just thought it would be good to move files to and from the machine.

Just in case someone knows the board, it is a Supermicro P5STE. Back in the day it was a pretty nice motherboard.

SanguinSE · July 28, 2019

Well, I'm not an expert, but removing the old battery seems like a good idea since once you plug in the motherboard to the PSU it will start trying to charge the leaking battery which sounds like a bad time. From what I could gather you should just be able to connect a new battery to the pins on the motherboard after you determine which pins to use. Sometimes there's a switch to select which battery to use, but the most likely scenario is that they are connected in parallel. A lithium battery should be fine as they are also rechargeable

I used to have a 386 25 MHz computer back in the day with a soldered on battery which eventually died, but since the CMOS doesn't reset until you pull the power cord I never actually replaced it. Just didn't seem worth the hassle.

tincanalley · July 28, 2019

12 hours ago, SanguinSE said:

Well, I'm not an expert, but removing the old battery seems like a good idea since once you plug in the motherboard to the PSU it will start trying to charge the leaking battery which sounds like a bad time. From what I could gather you should just be able to connect a new battery to the pins on the motherboard after you determine which pins to use. Sometimes there's a switch to select which battery to use, but the most likely scenario is that they are connected in parallel. A lithium battery should be fine as they are also rechargeable

I used to have a 386 25 MHz computer back in the day with a soldered on battery which eventually died, but since the CMOS doesn't reset until you pull the power cord I never actually replaced it. Just didn't seem worth the hassle.

The issue is if the replacement battery connection also expects to recharge the battery, I would have to use an NIMH replacement as lithium batteries require a different means of recharging. My understanding is the charge has to be closely monitored and this board wouldn't know that. Could be in bigger trouble than a leaky battery if it overcharges. Now if it doesn't try to recharge the external, an standard lithium would work. I guess I'm just going to solder a direct replacement as the MB manual mentions nothing about it and SM doesn't support anything over 15 years old and doesn't keep any files or other stuff on hand even if they wanted to help.