There must be some other boards available, but they're rather uncommon indeed. Check uh19 for boards that match your expansion slot criteria and look if you find any board with a cr2032 battery holder

I own a J-403TG v2.0, which you can find here.
It's powered by an OPTi 82C895, works great with DX2 and DX4, even 5x86 chips.
To get 3.3V chips working, you need to do a little mod (which I documented in the link above).
The chipset is a little picky on memory configs. You should use the manual to get it going right.
It has both AMI BIOS (from around 1993) as well as Award BIOS (from 1994).
Not exactly sure if it came from the factory with CR2032 (you may find it with barrel on auction sites), but the PCB does have holes for a CR2032 (which I used, works great).

Consider this as a "mini-review" 😀

The only other 486 VLB board with a CR2032 coin cell battery holder that comes to mind is the Asus VL/I-486SV2 range of motherboards.
However, as far as I'm aware, they all had Award BIOSes.

Another benefit of these Asus motherboards is that they also have a PS/2 header (connector), which was not very common on 486 motherboards (even on later PCI bases ones).

The Gigabyte GA-486VS (at least the revision 8A I have) has solder points for for a CR2032 battery, which can easily be installed as long as an SMD diode is removed to prevent it from being re-charged. It looks like factory-made when done.

But as with the ASUS board, it also has an Award BIOS. Is there a specific reason you are looking for one with the AMI WinBIOS?

However, as far as I'm aware, they all had Award BIOS

Which is a blessing.

AFAIK Aopen board AMIBIOS has problem with setting up dirty bit for WB L2 cache properly.

TheMobRules wrote on 2020-09-21, 15:26:

Is there a specific reason you are looking for one with the AMI WinBIOS?

Yep. 486 without WinBios is not a 486 to me. Childhood impressions and all that sentimental nonsense 😀.

I'm considering expanding the search by including anything with Dallas as well.

The Serpent Rider wrote on 2020-09-21, 16:00:

AFAIK Aopen board AMIBIOS has problem with setting up dirty bit for WB L2 cache properly.

Yes, although to be fair SIS471 boards with Award BIOS have the same problem. But with Modbin the Award BIOS can be easily modded to fix the dirty bit issue by changing a register (there was a thread about this on the forum). I also managed to fix the issue in the VI15G by using AMISetup, but that solution only keeps the updated register as a CMOS setting.

I honestly don't know how all those manufacturers managed to mess up that dirty bit setting, maybe there was some miscommunication between board makers, BIOS makers and SIS?

TheMobRules wrote on 2020-09-21, 16:53:

The Serpent Rider wrote on 2020-09-21, 16:00:

AFAIK Aopen board AMIBIOS has problem with setting up dirty bit for WB L2 cache properly.

Yes, although to be fair SIS471 boards with Award BIOS have the same problem. But with Modbin the Award BIOS can be easily modded to fix the dirty bit issue by changing a register (there was a thread about this on the forum). I also managed to fix the issue in the VI15G by using AMISetup, but that solution only keeps the updated register as a CMOS setting.

If you can track down the thread, please link to it - would like to know exactly how and where to change that register.

jesolo wrote on 2020-09-21, 19:16:

If you can track down the thread, please link to it - would like to know exactly how and where to change that register.

Re: 486 cache/ram speed issue with write-back

I have done the mod on both ASUS VL/I-486SV2GX4 and Gigabyte GA-486VS. Later today I can attach those modded BIOSes or some Modbin screenshots with details about which register to update.

TheMobRules wrote on 2020-09-21, 19:33:

jesolo wrote on 2020-09-21, 19:16:

If you can track down the thread, please link to it - would like to know exactly how and where to change that register.

Re: 486 cache/ram speed issue with write-back

I have done the mod on both ASUS VL/I-486SV2GX4 and Gigabyte GA-486VS. Later today I can attach those modded BIOSes or some Modbin screenshots with details about which register to update.

That would be great 👍

TheMobRules wrote on 2020-09-21, 16:53:

The Serpent Rider wrote on 2020-09-21, 16:00:

AFAIK Aopen board AMIBIOS has problem with setting up dirty bit for WB L2 cache properly.

Yes, although to be fair SIS471 boards with Award BIOS have the same problem. But with Modbin the Award BIOS can be easily modded to fix the dirty bit issue by changing a register (there was a thread about this on the forum). I also managed to fix the issue in the VI15G by using AMISetup, but that solution only keeps the updated register as a CMOS setting.

I honestly don't know how all those manufacturers managed to mess up that dirty bit setting, maybe there was some miscommunication between board makers, BIOS makers and SIS?

It's somewhat straightforward to modify 64KB AMI Color BIOSes in a hex editor to unhide settings. I've never attempted on a WinBIOS though. I suspect the WinBIOSes are compressed which complicates things.

alfer wrote on 2020-09-21, 16:32:

Yep. 486 without WinBios is not a 486 to me. Childhood impressions and all that sentimental nonsense 😀.

...and I thought I'd heard everything.

Thanks to Deksor's advice I was able to compile a list of mainboards that satisfy my criteria. I decided to include all the options with Dallas I could find as well. First post updated.

I have owned/own countless 486 systems, none of them Winbios. Amibios is the "bad boy" of 386/486 sytems. And Award is good and MR-BIOS is the holy grail.