If you're not familiar with vampire drain, it's when an electric car uses some of its energy while parked and not in use. An EV doesn't need to be "running" to use energy, and this can be a problem for people who have issues with range anxiety.
Essentially, every vehicle uses some energy while it's parked. However, this is more of a concern for EV owners since they're often very aware of the car's range, and they don't necessarily expect that range to disappear while their car is parked. It would be comparable to leaving your gas car parked for a few days and coming back to a gas tank that suddenly had noticeably less fuel.
