Vampire Drain
Vampire drain is the informal name for traction-battery energy lost while an EV is parked and not being driven or intentionally supplying an external load.
Why a parked EV can use energy
Connected services, telematics, security monitoring, key detection, battery and cabin thermal management, 12-volt battery maintenance, scheduled software tasks, and repeated remote-app checks can keep systems awake. Battery self-discharge also exists, but the observed loss at the dashboard can include vehicle loads, temperature effects, and changes in the state-of-charge estimate.
The drain is not one fixed percentage per day. It depends on vehicle design, software state, signal quality, temperature, settings, how often the vehicle is contacted, and how long it remains parked. Some vehicles enter deeper sleep after a delay, so a short observation should not be extrapolated linearly over weeks.
Owners can reduce avoidable drain by following the manufacturer’s long-term parking guidance and disabling unnecessary monitoring or scheduled features where appropriate. A large or sudden loss can indicate that a system is staying awake or that service is needed, but diagnosis requires vehicle-specific data.
For how parked loads fit into the wider energy and range picture, see Understanding EV Range.