I tried this a few times on my V3 with a CR2016 battery during the transition to the clock screen, and a sprite of Megatchi looking sideways appeared on the middle of the screen (something I've never seen on a Tamagotchi before, but it might be a sprite that's already used on the tamagotchi because I've only had Megatchi once) and then 2 black horizontal lines about 2/3 columns away from each-other appeared on the screen. While the battery was still inserted, the speaker kept making a constant faint "crackling" noise and the black bars were on the screen even after I took the batteries out, and even when I put batteries back in nothing happened and the black bars were still on the screen. At this point I was scared that I burned the screen or something but after leaving the batteries in for about 10 seconds the tamagotchi's lines faded slowly and it eventually turned on. I tried this a couple of other times but aside from the black bars and weird noise nothing else happened. Also, I tried it about 3 times on the shopkeeper screen but it didn't reset. KidRetro64's comment gave me some inspiration and when I have some free time I might try it on the same V3 on the connect screen, while it connects with a V3 and with a V4. If I find anything interesting, I'll comment here again with all the details.