Most all 286, 386 and 486 boards can run without a battery or with dead battery. Yes you will get cmos error so will have to set the bios options and save them.
As long as you do not turn it off those options will be saved even if rebooting many times...that is the only inconvenience....
Most 286 have an external battery connection (usually 4 pin) and you can use a 3 x AA (or AAA) 4.5v battery holder, I have a few that way and use Alkaline AA batts in a 3 x AA holder.
added: Only one of my boards prefers a 4 X AA 6.0v external bat, I would try with a 3 X and if cmos is not saved after power off then try 4 x...

Hi! 🙂 It depends on the motherboard, I would say.
Whether the battery is used as a buffer only or also as the main power source.
An real-time clock (RTC) has about the same power draw as a classic wristwatch.

Since the CMOS information is stored in a spare memory location of the RTC's RAM,
it's likely a necessity that the RTC is working in order to power-up the board.

Without the RTC active, the settings in Setup can't be stored to CMOS.
But even if the Setup and BIOS would ignore this, there's no information to read after a soft reset.
Unless the BIOS somehow used an area of system memory to store a copy of the settings.
But why should it do this in first place?

Excelsior wrote on 2022-10-15, 16:19:

I have an older 286 motherboard with a barrel battery. Since the barrel battery was dead and started to leak I removed it and cl […]
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I have an older 286 motherboard with a barrel battery. Since the barrel battery was dead and started to leak I removed it and cleaned the board.
But before putting it in a computer, my question is the following: will the motherboard function normally without the barrel battery or a more modern (and less dangerous) CMOS battery?
Is there a risk or an inconvenient if I use this motherboard/computer without any CMOS battery at all?
Besides the CMOS data loss (obviously) are there any other problems that could arise?

I have come across boards that will not post when the Dallas dies.