From what I can recall of high-school chemistry, it depends on which ions are being used, and generally different for each combination. The basic zinc-manganese dioxide cell has an EMF of about 1.5V, while lead-acid car battery cells give about 2V.

https://www.pveducation.org/pvcdrom/battery-characteristics/...

https://www.pveducation.org/pvcdrom/battery-basics/electroch...

Update: I see it also depends on their concentration, so the voltage changes as the cell discharges, unless all the components are solids:

https://www.pveducation.org/pvcdrom/battery-basics/nernst-eq...

When I say classic, I meant the classic from 1800's, you know when Volta, Faraday and other were experimenting with different wet/dry electrolytes between the zinc/copper discs. Citric acid as electrolyte holds 1.2V and is easy to buy from you local supermarket.

https://en.wikipedia.org/wiki/Voltaic_pile

So there you have a third datum confirming that the voltage is dependent on the materials used.

The classic cell has 1.5V.

The classic is this one:

https://en.wikipedia.org/wiki/Voltaic_pile