The stuff inside the screen is either LCD (liquid crystal display) or LED (Light emmiting diodes) Because i opened mine up because it brokes and there were rubbery things and when i put 2 batteries on it, the screem lit up
Your Tamagotchi is warning you that the batteries are low. Change it within 10 secs of taking the battery out and you'll keep the tama u had aswell. Don't worry.