P1s have no memory function, so changing batteries will lead to a lost tamagotchi. If you're up for the challenge, you can try quickly changing the batteries. Vintage tamagotchis don't die immediately when batteries are removed - you have 3 - 4 seconds while the screen dims before it dies entirely. If you remove the back screws whilst pressing the back panel down firmly, you might be able to swap the batteries fast enough to keep your character. I've done this a few times successfully, and a few times not so successfully, so no guarantees