At this point, everyone knows that EVs have a big traction battery, typically placed at the bottom of the car and filled with lithium-ion. This acts as a power source for the electric motor that drives the wheels.

What most people don’t know is that most EVs (yes, there are exceptions) still keep the traditional 12-volt lead-acid battery (this includes the new Nissan Leaf, see below photo). This 12-volt battery still powers the car’s accessories such as the radio, climate control, and so forth. Sadly, like its internal combustion counterpart, if this battery goes dead, it will prevent your EV from running.

But won’t the big-ass battery continuously charge the 12-volt lead acid battery? Well, glad you asked. Typically, EVs will charge their 12-volt lead acid battery when it’s in “Ready to Drive” mode—idling in ICE parlance, or when the car’s being driven. Some will also draw charge from their traction battery to charge the 12-volt battery, but only if the traction battery’s charging and not just plugged in (it stops charging the 12-volt battery once the traction battery reaches 100 percent charge).

In other words, for would-be EV owners, including the Leaf, simply leaving their cars plugged in during long periods of non-use may not be enough to care for the 12-volt battery. It’s highly suggested for EV owners to either keep their cars “running” but not plugged in periodically to keep the 12-volt battery charged up, or do what owners of gasoline- and diesel-powered cars do: invest in a trickle charger such as CTEK.