Electric cars, just like every other device or machine that relies on rechargeable batteries, slowly discharge over time. Leave them in low state of charge for too long, and their traction battery packs are destroyed.
Which is why automakers like Nissan and Chevrolet recommend owners follow specific instructions before leaving their Nissan Leaf and Chevy Volt cars for extended periods of time.
As we’ve proven, a 2011 Nissan Leaf will lose a few miles of charge if left unplugged in a semi-charged state for 8 days.
Leaving your car plugged into a suitable charging station while you’re away might seem like a sensible solution, especially if you time charging to finish just as you return.
There are two batteries
But as some Nissan Leaf owners over at MyNissanLeaf.com have discovered, leaving your Leaf plugged in while away could drain the car’s other battery -- the one that runs its 12-volt accessory circuits.
Returning to their cars after a vacation or time away, these owners are reporting that their Leafs are unresponsive and often won’t unlock.
2011 Nissan Leaf SL
Just like almost every other car on sale in the U.S. today, cars like the 2012 Chevy Volt and 2012 Nissan Leaf have 12-volt accessory batteries that provide power to run onboard computers, entertainment systems, lights and wipers.
In a gasoline car, its 12-volt battery is kept charged by an alternator, powered by the car’s engine. In an electric car, a high-power dc-to-dc converter keeps the battery fully charged, fed by power from its traction battery pack.
In a car like the Nissan Leaf, its 12-volt battery will gradually discharge as it provides power to always-on systems like the alarm, locking system, radio and telematics computers.
When it gets too low and the car is unplugged, the Leaf’s 12-volt solar panel or dc-to-dc converter kicks in to charge it back up.
If the Leaf is plugged into a charging station and drawing power to charge its on-board traction battery pack, it should also charge up the 12-volt battery.
But when plugged into a charging station that is not actively charging the car, the Leaf enters into an operational mode that continuously looks to communicate with the charging station, drawing power as needed from its 12-volt accessory battery.
In this mode, the extra power drain can flatten the 12-volt battery -- not the traction battery -- in under a week.
2011 Nissan Leaf SL
Nissan Leaf guru Phil Saddow has spent some time looking into the issue, using his own 2011 Nissan Leaf as a test subject.
On the MyNissanLeaf forum, he advises owners who are going away on a long trip to plan their car’s vacation with care. “Leaving a charge cord plugged into the Leaf, but not charging, will leave the ECUs awake and cause more than normal load on the 12v battery. Don’t do this if at all possible!,” he warns.
“Leave the charge at 50-80%,” he advises. “Do not leave anything connected to the charge port. If you are leaving for longer, charge to 80% and then disconnect the negative lead on the 12v battery or ad a “Battery tender” type trickle charger. “
Other suggested solutions include setting charge parameters to execute an 80 percent charge every day for a few minutes, ensuring that the 12-volt battery always gets some charging opportunities every day.
We’d like to offer one more solution: Lend your electric car to a trusted family member or friend while you’re away, and let them experience the joys of zero tailpipe emissions driving.
2012 Nissan Leaf 4-door HB SL Headlight
If the worst happens however, and you return to a Leaf with a dead 12-volt battery, there is a solution: jump-starting. Similar to jump-starting a regular car, connecting another car battery to the Leaf's 12-volt battery, taking note to observe the correct polarity, can provide enough power to start the car. Provided there is power in its traction battery pack, it should then be possible to use the car as normal.
In its official Leaf manual, nissan advises "If it is not possible to turn the system on by following this procedure, contact a knowledgable Leaf repairer such as a Nissan certified EV dealer immediately."
It's also worth noting that while most other green cars, like the 2012 Toyota Prius, should not suffer this problem, and that as far as we are aware, this problem is peculiar to the Leaf.