This is the key. I'm running a 6 years old galaxy tab s2 for reading at night, about 10 to 30 minutes a day, with an OLED display in airplane mode. Due to the d

This is the key. I'm running a 6 years old galaxy tab s2 for reading at night, about 10 to 30 minutes a day, with an OLED display in airplane mode. Due to the display and white-on-black colors, only standby really contributes significantly to the power consumption. Still, even though the battery is very old by now, with average use, the battery indicator is usually at around 60 % at the end of a week without charging.