On Wed, 6 Jan 2021 10:40:30 -0800 (PST), "Peter W."
wrote:

My guess is that it is a 2032 button cell - which have been popular for that function for a long time. Are you able to apply about 3V at the appropriate polarity and see if the memory comes back? Or even 1.5V as proof-of-concept?

After which comes the question of whether it is rechargeable (LIR2032) or not (CR2032).

I was thinking *if* it is rechargeable, I *could* (could I not?)
replace with an equivalent non-rechargeable in series with a diode to
prevent it from taking a charge it's not designed for?