The Nissan Leaf electric car and Chevy Volt plug-in hybrid went on sale within days of each other back in December 2010.

Now, we're expecting second-generation versions of both cars for 2016--and each will have significant upgrades.

The most significant upgrade to the Nissan Leaf will be a choice of battery-pack sizes, meaning more range than the car's current 84 miles.

Nissan product chief Andy Palmer told Green Car Reports that he could envision two or even three different pack sizes, giving buyers the option of paying more to get greater range--possibly 120 miles, maybe closer to 150 miles.

That could give the top-level Leaf about three-quarters the range of a low-end Tesla Model S. If its price were around $35,000--just half the cost of that Tesla--we think a lot of buyers would consider Leafs who now say 84 miles is just too little.

2014 Chevrolet Volt

2014 Chevrolet Volt

The 2016 Chevy Volt is likely to be launched at next January's Detroit Auto Show.

It will ride on an all-new platform shared with the upcoming 2016 Chevy Cruze compact sedan--just introduced in China--but stick to the general shape of the current Volt, freshened up.

We expect the range of the Volt to stay around where it is today--it's rated at 38 miles, so we figure no more than 45 miles to come.

The advance here is that its battery pack will be smaller, and a lot less expensive, meaning the Volt might break even for the company as it ramps up volume.

We hope Chevy is able to add a fifth seat, or a second, more upright Volt body style better suited for families. The lack of that fifth seat has been a dealbreaker for a lot of Volt shoppers.

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