The Basic Math of Home Charging Needs

When we bought our Nissan Leaf, the dealer sales representative told me that Nissan recommended level 2 home charging system. But based on my personal experience and research, this is an unnecessary expense for most people.

A level 2 home charger allows you to rapidly re-charge your electric vehicle. The typical cost is $400-$500. However, most home garages don’t come equipped with a 240V 40 amp circuit. Costs to provide 240V service will vary widely depending on where your panel is located relative to the place you need to install the charger. Installation might add a few hundred bucks but might be closer to $1,500.

To determine if a level 2 charger is worth it, simply estimate how many miles you drive on a daily basis and how long you can charge while at home.

Based on initial experience and some simple math, I concluded that the standard 120V household outlet (20 amp circuit) in my garage with the basic level 1 cord set that comes standard with the car would be just fine. One year of experience with zero anxiety has proven me correct.

When driving, I get an average of 4.2 miles per kilowatt hour (kWh). Typically, I drive 35 miles per day, which means it takes about 8 kWh to charge my car battery enough for daily use.

A standard 110-120V household outlet charges typically at a minimum of about 1.4 kW per hour. So I need about 6 hours to charge my battery enough for my daily drive.

Let’s say you need to drive more—maybe 50 miles. And you’re also getting lower mileage per kW—maybe 3 miles/kW due to driving more aggressively, commuting mainly at high speeds or using your air conditioner or heater extensively. You would need 12 hours to replenish your battery to that range. You likely still could accomplish this with a standard 120V outlet at home. If you have workplace charging, you might top off your battery during the day.

What if you need to drive 60 to 70 miles or more some days…won’t you need a faster charger at home? The answer depends on how often you drive that far and whether you have convenient access to charge away from home on those days.

Level 2 chargers replenish the battery considerably faster than level 1, up to 7.7 kW/hour. However, the vehicle’s on-board charger may limit this. My Leaf can charge up to 6.6 kW/hour. So if I needed to replenish 70 miles of range with a level 2 charger, it would take less than four hours (compared to 16 hours and 40 minutes with a level 1 charger). If you drive that far regularly, you might consider level 2 at home.

But another option is to swing by a public charging station on those days when extra charge is required. I do that on occasion. When I do, typically, I need to add 10-20% of battery capacity, which takes five or ten minutes. Some public charging stations are free. Others might cost $5 or so for 5 minutes plus $1 per minute after that. You find public stations on the PlugShare or another mobile app or your car’s own stations map.

For someone purchasing a plug-in hybrid such as a Chevy Volt, Ford C-Max or other vehicle with shorter all-electric range, level 2 home charging would rarely, if ever, be justified based on the extra cost. For a full battery electric car, I argue it’s also rarely justified.

The bottom line is that many prospective or new EV owners end up spending extra money unnecessarily on home charging systems. Don’t ask yourself, “How long will I need to charge from a dead battery to full?” The more relevant question is, “How long will I need to charge in order to replenish typical daily mileage needs?”

So before you spend money on what may be an unnecessary device plus installation, think carefully about your typical daily needs and do some basic math. Enjoy your new electric vehicle!

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