I never had a Tamagotchi, but the little rectangular Digimon versions of them were all the rage when I was like 8. I kinda miss those things.
And I recall a year or two later getting another toy...may or may not have been Digimon branded...that had the same connector on the top, but was more rounded in shape. I remember after my battery on one died, holding the two together to try and keep it alive through the power the other one was sending it. Of course it only worked as long as I was physically holding them, and would then reset.