Most drivers know how easy it can be to accidentally leave a vehicle’s radio or lights on when it is parked and not all cars automatically switch off these components at the same time as the engine. If left on for long periods, especially overnight, it can vastly reduce the charge of the battery or flatten it completely. Even if a car does start after leaving an electrical source on, it is likely for a problem relating to severe discharge to occur later down the line, and probably when it’s most inconvenient.
If a vehicle is not used for long periods, the battery will become deeply discharged and this can easily cause permanent damage to it. This issue is common in vehicles which are left in storage for more than six months, such as vintage cars and motorbikes as well as boats and farm vehicles, but some chargers can be safely left connected for years, repeatedly topping up the charge to the target level.
While there is little chance of a fully charged modern battery freezing, batteries which are deeply discharged can be at risk. Older batteries, which are coming to the end of their lifespan, are less likely to be able to handle the extreme temperatures. Therefore, it’s always a good idea to fully charge the battery and carefully clean the exterior and terminals when the weatherman says the below zero temperature will hit double figures.