We use the battery analogy to explain life living with a chronic illness, especially those that are invisible.
Every single thing we do costs us energy. Something seemingly simple, like getting up and getting dressed can take up a ton of charge leaving us rationing energy for the rest of the day. On high-pain days, our batteries are depleted even faster. Some days we can recharge through some rest or borrow charge from the next day, but it's always being considered. As Chargies we don't have the luxury of living life without considering how much charge we have left.
(The Battery Analogy was originally written by Natalie van Scheltinga, the founder of The Unchargeables. We now call ourselves The Chargies!)