Replacing CMOS battery on motherboard

[Greegor]

[...] CR2032's have to last all on their own,
no charging allowed. The max charge current allowed is 1 microamp,
so they're serious about allowing current to flow into them.
Current may only flow out.

A 3+ Megohm resistor would work then.

That tiny of a trickle charge might make a BIG difference.

I've seen SEVERAL mothballed systems with CR2032
batteries where resetting the clock, shutting them down
and then checking them later indicated their RTC was
running slow when the system was off.
Leaving them on for 4 hours or so SEEMED to
charge the CR2032 because the RTC began to
keep time accurately when systems were off.

Is it possible they actually implemented the
1 microamp trickle charge you implied?

I've actually seen this trick work several times.

I've also seen systems where the BIOS settings
were "forgotten" due to low battery and running
it for a day caused the battery to hold the settings.

Even if they used a 6 Megohm resistor to
charge the CR2032 battery at half a microamp I would
expect that would be enough to make a big
difference to that tiny battery.

Is there a reason that flash hasn't
replaced CMOS for BIOS settings?