A battery monitoring device monitors a lithium precipitation amount in a lithium ion battery. The battery monitoring device includes a precipitation amount detection unit that has a short circuit for discharging the lithium ion battery by temporarily shorting both ends of the lithium ion battery. The lithium precipitation amount detection unit calculates an estimation value of the lithium precipitation amount based on a change in at least one of current or voltage when both the ends of the lithium ion battery is shorted by the short circuit. The battery monitoring device includes a temperature sensor that detects a battery temperature of the lithium ion battery.