I have two cell phones, one is for work the other is personal. I had them stacked on top of one another on my desk. All of a sudden my work phone went completely dead from about 75% full, and my Android went from 85% to 32%. What gives?
It's winter, your phone was probably very cold. I've had problems like that too. My phone went from 6% to dead. Then I heated it back up to room temperature, turned it back on and it was at 26%. If it was a normal condition, and it happens again, consider replacing your battery.