It's a fairly common practice for internal-combustion cars to be offered with multiple engine and transmission options.
But it is far rarer for electric cars to be offered with different battery-pack alternatives.
Right now, in fact, only two manufacturers offer multiple battery options on production electric cars.
Those two companies are Nissan and Tesla.
Tesla started the practice, and since 2012 it has offered—or discussed offering—myriad battery-pack sizes on its electric cars.
It originally planned to offer 40-, 60-, and 85-kilowatt-hour battery packs on the Model S, but the 40-kWh version was never produced due to what the company said was extremely low demand among its buyers.
2016 Tesla Model S P90D and Boeing 737 drag race
The surviving 60- and 85-kwh options eventually transitioned to the current Model S offerings of 70 and 90-kWh packs.
The 70-kWh pack yields an EPA-rated 234 miles of range in the rear-wheel drive Model S 70, and 240 miles in the all-wheel drive Model S 70D.
The 90-kWh pack is only available with all-wheel drive, allowing for 270 miles of range in the Model S 90D, and 253 miles in the Model S P90D performance version.
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Meanwhile, the Tesla Model X crossover SUV was originally slated to be offered in 70D, 90D, and P90D versions.
But Tesla replaced the 70D with a 75-kWh 75D model before any examples of the former were produced.
The 75D achieves an EPA-rated 237 miles of range, compared to an estimate 220 miles for the withdrawn-before-birth 70D variant.
2016 Nissan Leaf
The Model X 90D is rated at 257 miles of range, while the P90D is rated at 250 miles.
Tesla has said the upcoming Model 3 sedan will have a "minimum" of 215 miles of range, hinting that multiple battery-pack options may be offered on that lower-priced model as well.
Nissan's range of options isn't quite as lengthy.
MORE: BMW i3 Electric Car To Get Longer Range Next Year, CEO Says (Oct 2015)
For the 2016 model year, Nissan added a 30-kWh battery-pack option for the mid-level Leaf SV and top Leaf SL models.
The base Leaf S continues with the original 24-kWh pack.
Models with the 30-kWh pack are rated at 107 miles of range, while 24-kWh versions have 84 miles of range.
2016 BMW i3
Multiple battery-pack sizes allow both Nissan and Tesla to offer electric cars over a wider range of prices and let buyers choose a vehicle more closely suited to their specific needs.
So far, though, other carmakers haven't shown much interest in adopting this model.
The 2017 BMW i3 is expected to get a range increase, likely from an increase in pack size.
BMW could offer the larger pack alongside the current, 22-kWh pack, speculates i3 advocate Tom Moloughney in a blog post.
Harold Krüger—BMW's CEO—first mentioned the range increase in October, but so far there has been no official public discussion of multiple battery-pack options.