Battery Range
So, how far CAN you go in an electric car?
The short answer is as far as you need to go. The longer answer is 4 miles per kilowatt hour of usable battery.
When I originally built the Electric Geo Metro, it really was only designed with about a 20 mile range in mind. I know that doesn’t sound like much, but the grocery store is only a couple of miles away, and I was working in a downtown office only a few miles the other direction. In fact, 20 miles was actually plenty of range for what I needed. That car was also running on USED lead-acid batteries. While it was pretty short range, it was also a great DIY project, and very affordable. (About $1,300 for the ENTIRE project.)
Over the last decade, the cost of lithium batteries has dropped tremendously. In fact, anyone NOT using lithium batteries now for a conversion better have a darn good reason for NOT using them. (“I got this pallet of brand-new lead acid batteries FREE!” No joke, that actually happened to a friend.)
Whether you are using lead-acid, lithium, or any other flavor of battery, it turns out that many electric cars all use about the same ballpark number in energy use – 250 watt-hours per mile, or 4 miles per kilowatt hour. It’s a good estimate to use for planning your project. Just take the usable size of your battery pack in kWh, multiply it by 4, round down, and that’s your approximate range in miles for good weather mixed-use driving. Keep in mind that driving fast lowers your range, as does using other energy draws, such as cabin heating in the winter. (I’ve seen winter use of electric cars hit as high as 500 wh/mile or 2 miles per kWh.
The original generation Nissan Leaf used a 24kwh battery pack and had a 84 mile official range. The Chevy Bolt has a 60kwh battery and an EPA range per charge of 238 miles. A Mitsubishi iMiEV has a 16 kWh battery, and sports a 62 mile official range. I hope you are seeing a pattern here. Approximately 4 miles per kilowatt-hour.
How far would you want your DIY electric car to go?
Divide that number in miles by 4 to get your battery pack size in kWhs. Did you want to go 300 miles per charge? Hmm. That’s going to be a very large and expensive battery pack! (One reason why a Tesla P100D costs so much!) Electric cars are really best with an APPROPRIATE size battery pack. That’s the distance you want to go MOST of the time. Using a “not too large” battery saves not only cost, but also the space needed in the vehicle for the battery, as well as unnecessary weight.
As for exceptionally long distance trips, rather than having a huge battery, it’s often a better choice to use quick charging, driving a Plug-In Hybrid (Chevy Volt, Prius Prime, etc.) or heaven forbid – use a gas car!
All sorts of batteries are now available both by mail order retailers AND through the secondary automotive market. That means salvage yards. It’s amazing how a person can now go to a junk yard and buy a battery from a crashed Nissan Leaf or Chevy Volt. Both have great cells for hobbyists and DIY’ers!
Lastly, if you are building an electric motorcycle, the rule of thumb is typically 100 watt-hours per mile or 10 miles per kilowatt-hour. On my Vectrix electric motorcycle, I installed used Nissan Leaf cells for a total theoretical capacity of 9kwh. So, I should be able to go 90 miles per charge. Could I actually do that? Yes and no. For one thing I wasn’t using quite the full capacity of the battery. (I didn’t charge to the maximum voltage, nor discharge to the lowest recommended voltage.) The other other thing is that I wouldn’t get that range driving fast all the time. One week, I was mostly in town, so I just kept riding the cycle and not recharging. By the end of the week, I actually did get to 90 miles on a single charge, but in normal use, it was closer to 70. Again, keep in mind that 4 miles/kWh for a car and 10 miles/kWh are just tools for estimating. Always design your project so that you have the amount of range you need, and plan for other energy use such as heat or air conditioning.
As always, “Your mileage may vary!”
{ 2 comments… read them below or add one }
I wondered what you do for interior comfort, but I guess you didn’t include AC or heat in this project. Woould you have room under the hood to include a compressor, etc for AC? Rolling a window down in summer and up in winter wouldn’t do it for me. Another thing I have always wondered about is what do you do if you deplete the batteries while in transit. I take it you can’t just pull in to the nearest outlet and plug in to recharge even if you wouldn’t necessarily need a full charge to get home, call for a wrecker to tow you home? How long does it take to top off a charge from near zero? Would there be a way to switch from series to parallel and limp home at slow speed if you knew you were getting to a low charge? I assume you run the lights from the battery under the hood, right? You do a good job of explaining what is being done. The videos are all well done. I’m afraid I wouldn’t be able to tolerate a low number of miles in the “tank” in a single vehicle since I like trips in excess of 50 miles one way. With a second vehicle that was electric for “around town” driving, I could do OK, though. Thanks for the info and great videos.
Hi Ron,
The Geo Metro did NOT have air-conditioning to start with and I didn’t do anything to add it.
Heating is covered at this post: https://300mpg.org/projects/electro-metro/heat/
Among some of the little tricks I did with the car was that I added brackets to the front of it so that it could be flat-towed behind a my pickup, just like how some RVs tow a car behind them.
I moved the car a few times that way to get it to a friend’s place to work on and also to some car shows. I don’t remember ever having to tow the car because of running out of battery or other problems.