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.
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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The 75D achieves an EPA-rated 237 miles of range, compared to an estimate 220 miles for the withdrawn-before-birth 70D variant.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.
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