Batboard

While doing a battery date code survey on our portables, I noticed that while most of the radios only have 2 gold contacts to connect to the battery, some had 3. There didn't seem to be any discernible pattern based on exact model or country of origin. I can't find anybody who knows why. I also noticed that while all the gang chargers have 4 contacts for the batteries, the single unit rapid chargers mostly have 3 with only the occasional 4.
Are these just production variations, or is there a meaningful difference here?

I believe it's more production related. The three MTS2000s I have, have both. An older model has three and the two newer models have two. I thought at one time it was related to being FM approved but all three are FM approved.

And the additional charger contact is for the battery's internal thermistor.