You can choose from two or more engine and transmission options in most gasoline cars, so why not offer a choice of battery-pack sizes in hybrids and plug-in electric cars?

That was the question posed by the launch of the Tesla Model S, which was originally offered with three different battery capacities.

Now the notion of optional battery upgrades seems to be spreading.

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There are persistent rumors that the 2016 Chevrolet Volt range-extended electric hatchback will offer at least two battery options: one for the original range of roughly 40 miles, but a lower-range option of perhaps 25 or 30 miles to reduce the sticker price.

And the 2016 Toyota Prius is also rumored to offer two battery packs, a standard nickel-metal-hydride pack delivering a combined rating of 55 miles per gallon and an optional and pricier lithium-ion pack that could give a 60-mpg rating.

The optional pack might also be connected to the plug-in hybrid version of the 2016 Prius, which Toyota has said will have a higher electric range than the current model's anemic 11 miles (with only 6 miles continuous even on the relatively gentle EPA test cycles).

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Tesla set all of this in motion when it launched the Model S electric luxury sedan with a choice of battery packs of 40, 60, or 85 kilowatt-hours.

It soon cancelled the 40-kWh model, saying that there were so few orders for it that it didn't make sense to continue the model.

The majority of Model S buyers continue to specify the largest battery size, indicating that if a larger 110-kWh battery is introduced for the Model S, as rumored, it should find a healthy market too.

2012 Toyota Prius Plug-In Hybrid, Catskill Mountains, NY, Oct 2012

2012 Toyota Prius Plug-In Hybrid, Catskill Mountains, NY, Oct 2012

Meanwhile, a new German study indicates that offering a choice of battery sizes could expand the overall market.

That study was neatly summarized by ChargedEVs last month, and it's worth a read.

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