If I have to go get the model number I will. But maybe it happens on many models? What is this green filled small battery icon trying to tell me? It's never appeared before until lately. I'd say the TV is more 8 or 9 years. But it's a flatscreen with many ports. A Chromecast is plugged into the HDMI but the power to it has been unplugged for several years? I'm clueless! Anyone else have this?
I will guess that since the TV has been unplugged for years the standby battery or capacitor in it has lost its' charge. The indicator may show that it is charging up or that their is a problem. The TV would still work normally but if you unplugged it the settings might revert to the defaults.
Search online for the owners and service manual for that TV. The info you need should be in there.