NEW YORK (TheStreet) -- I spent a week and 420 miles driving Porsche's (POAHF) first car with an electric motor and a wall plug, the Panamera plug-in hybrid. How does it measure up against Tesla, BMW, Cadillac and all the other plug-in cars in the market?

For starters, the Porsche Panamera is a unique and extreme car in its own right, regardless of this most recent version with an electric plug and motor. It is wide, low, has decent rear seat space and corners as if it was born and raised on a race track.

However, the purpose of this review is not to focus on the overall car but mostly on the Panamera's electric motor, transmission, braking, accelerator calibration and plug-in charging characteristics. In other words, how does it deliver as an electric car?

The Panamera plug-in's base price is $99,000, although the car I drove had a sticker of $128,505. It combines a 3-liter, 6-cylinder engine with a 95-horsepower electric motor, both mated to an 8-speed automatic transmission.

It offers 16 miles of electric range, if driven very gently, and after that the efficiency is on average 25 miles per gallon. If your driving distances are mostly shorter than 16 miles, you can go on electricity almost all the time. On some days, I yielded 588 mpg and 261 mpg as examples, having charged three times a day, in whole or in part.

588 mpg in a Porsche? That's a headline right there!

There are many dimensions of how one should evaluate a plug-in electric car, whether pure battery-electric or gasoline-electric hybrid. Regardless of the type, however, what any plug-in car has in common is that it has to deliver supreme smoothness in its power delivery. Driving an electric car should be smoother and more relaxing.

What are the dimensions to this smoothness? It's all in the pedal control and lack of shifting. You should rarely have to touch the brake pedal because when you let go of the accelerator, regenerative braking decelerates the car for most everyday needs. Pressing the accelerator should yield a seamless acceleration from the first millisecond.

It is in this task to deliver a seamless and smooth electrified drivetrain that the Porsche Panamera fails. It is not the first 8-speed electric car I've driven. I drove the prototype of the BMW X5 plug-in hybrid a couple of months ago.

However, the Porsche 8-speed automatic makes for a relatively jerky drivetrain experience. Unlike all other plug-in electric cars in the market, it is neither seamless nor smooth. For a while I wondered whether the gasoline engine was on or not. Only when I realized the tachometer was sitting still at zero did I believe that the gasoline engine hadn't come on.

Then we have the issue with the brake pedal and accelerator pedal themselves. They are very hard to modulate to make for the smoothest experience. Whether you're accelerating or braking, the car stutters relatively compared to other electric cars.

And braking all the time you will do, compared to those other electric cars. Why? Because the degree of regenerative braking is very mild. This is the opposite of a Tesla(TSLA) - Get Report or BMW i3, as they are the best examples of great regen braking.

Compared to all the other electric cars, the Panamera simply doesn't give you that trademark electric motor smooth experience. You feel like the car is working against you instead of for you. It's a little bit like walking a big dog that's trying to run in the wrong direction at almost all times, versus one that's working in harmony with your own walk.

From an architectural standpoint, the Porsche actually comes the closest to the Ford(F) - Get Report Fusion and C-Max Energi models. The main difference is that they lack the 8-speed transmission, in favor of a seamless one. They both provide a smoother experience.

What the Porsche does a little bit better than the Ford models is that it stays in electric mode more consistently than the Fords. They would sometimes fire up the gasoline engine for no good reason.

In terms of plug-in hybrid drivetrain smoothness, the Porsche doesn't hold a candle against General Motors'(GM) - Get Report Chevrolet Volt and Cadillac ELR. I drove the Volt immediately before and after the Porsche and it's an infinitely smoother and much more powerful experience (in electric mode, not when the Porsche's gasoline engine fires up).

This speaks to the fact that the Porsche is a very different kind of so-called "compliance car." You see, there are two kinds of compliance cars. One is the kind that's sold only or mostly in California to meet regulatory requirements there. They are mostly pure electric, and mostly very powerful.

The other kind of compliance car is one that's meant to circumvent European so-called congestion charging in cities such as London. This means outfitting the plug-in hybrid with a weak electric engine that can go 30 miles on the very generous European test cycle. The U.S. EPA test cycle can yield a result as little as half the European range/mileage.

The result of this Porsche fitting into this European compliance car envelope is that the electric performance is sub-par, and doesn't compete with the far more capable offerings from Chevrolet, Cadillac, BMW, Tesla and others. Some companies such as BMW offer both kinds of approaches.

There are other details that speak to how Porsche hasn't yet delivered a competitive plug-in electric experience. Specifically, charging comes to mind.

For starters, the indicator to the charger is hidden next to the charging port itself, and the only way to see it is to walk up to the car and look closely. Porsche needs to learn from the Fiat 500e here. The indicators need to sit high up, where they are visible on the car, from inside the cafe, from almost any angle, even if you are wearing polarized glasses.

Second, the charger itself is extremely heavy and bulky. It is a horrific pain to move around, and it doesnt wind up on itself just like the offerings from GM, Ford and others. It comes in a bag so large that I'm not sure it would be legal carry-on for a domestic flight.

Third, the grounded 3-pin, 110-volt connector is upside down, making it hard to fit in many places, and makes me afraid it might break the connector. Who thought of this?

When one presses the "unlock" button on the key fob, the car stops charging. You might have just started charging and then realized you needed to get something else from the car. Now you have to unplug, swipe your card again and plug in again. I don't know any other plug-in car with this usability mistake.

I liked the instrumentation reasonably enough, slightly better than the industry's low standards. That also means it's something like 25 years behind the Tesla in terms of almost all aspects.

The front seating position is very good except for when driving without shoes. The accelerator pedal stands so straight up and requires so much force that one needs to sit so far up front, causing the knee to rest against the instrument panel. Clearly not good.

The bottom line is this: As a plug-in electric car experience, the Porsche Panamera is a disappointment. Every single plug-in electric car I've driven is smoother, and most are much more powerful in electric mode.

Tesla has nothing to fear from Porsche yet. The BMW i3 drives infinitely better and costs half. Perhaps the most direct competitor in terms of overall car body -- the Chevrolet Volt -- absolutely smokes the Panamera in smoothness and all-electric power, while costing a third as much. From the luxury competition, the Cadillac ELR is vastly better electric car and it still costs a lot less than the Porsche.

I've driven them all, and it's clear that Porsche has some serious homework to do on the plug-in electric car front. I assume the company is hard at work in the R&D labs and we may see dramatically better plug-in electric cars from Porsche in and after 2016. We'd better.

At the time of publication the author had no position in any of the stocks mentioned.

This article represents the opinion of a contributor and not necessarily that of TheStreet or its editorial staff.

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