Sales of the Chevrolet Volt, left, fell behind the Nissan Leaf for the first time this year.

After charging up for the first 10 months of the year, sales of the Chevrolet Volt plug-in hybrid unexpectedly short-circuited last month.

Volumes fell to barely half of September and October levels – ensuring that Chevy will end 2012 selling barely half as many Volts as it had originally hoped for this year. The plug-in’s sales for November fell behind those of two key rivals, the Nissan Leaf battery-electric vehicle and Toyota’s Prius Plug-in. But all three models appeared to lose some momentum despite the overall surge of the U.S. car market.

Even so, Chevrolet officials downplayed last month’s weak performance and ascribed it to inventory issues. The maker has twice halted production at the Volt plant in Detroit since spring, most recently between mid-September and mid-October to re-tool the facility to also handle production of the next-generation Chevrolet Impala.

Toyota's Prius Plug-in was the top-selling advanced battery-car in November.

If anything, Chevy dealers are struggling to meet demand for the Volt, insisted the division’s General Manager Don Johnson. “Dealers are just clamoring for more,” he insisted during a conference call.

According to Johnson, Volt inventory has actually risen from an eight to 23-day supply – but that is still barely a third of what is considered the normal amount dealers like to have on showroom floors.

In fact, November’s sales numbers were a case of half-empty/half-full.  Compared to year-ago levels, sales actually were up 33%, to 1,519 vehicles. But Chevy sold 2,851 Volts in September and 2,961 in October, capping a steady rise this year.

Part of that surge appeared to reflect California’s approval of the updated 2013 version of the Volt. It now qualifies for the state’s much-coveted HOV, or commuter, lanes even with just one person aboard.

Through the end of November, Volt sales totaled 20,828 – meaning the plug-in should end the year somewhere in the 22,000 to 24,000 range, depending upon how many vehicles can be delivered to dealers and then to customers. That would more than double 2011 sales but fall well short of the earlier goal of 45,000 this year.

Other factors may have contributed to Volt’s November shortfall. For one thing, Chevrolet trimmed back incentives on the plug-in last month. Meanwhile, the market has suddenly seen a glut of competing models arrive at dealerships. That includes the Prius Plug-in as well as Ford’s new C-Max Energi plug-in. There are a number of new battery-electric vehicles, as well, such as Ford’s Focus Electric.

And even more new products are coming, such as Honda’s Accord plug-in and its battery-electric Fit subcompact. Chevy is preparing to launch the Spark EV and its up-market cousin, Cadillac, will soon introduce a luxury version of the Volt, the Caddy ELR.

Toyota has been rapidly gaining ground since the launch of the Prius Plug-in, sales reaching 1,766 units last month – and 11,389 in all since its mid-year launch. The Toyota model has barely a third the battery range of the Volt but at $32,000 it is $7,145 less than the sticker on Chevy.  (The gap is actually smaller after federal tax credits, however. Due to its larger battery size, the Chevrolet Volt qualifies for a $7,500 credit, the Prius only $3,750.)

The Nissan Leaf has also been regaining momentum in recent months after an unexpectedly slow start of the year.  The Japanese maker sold 1,539 of the battery cars in November, down just 40 from the month before, but more than double the 672 it sold in November 2011.

Nissan had insisted its earlier sales shortfall was also the result of inventory problems. The maker will have no such excuses going forward. It is planning to launch production at a second Leaf plant in Smyrna, Tennessee this month.

The maker is also planning to launch a new lower-cost version of the battery car in mid-2013.