Prius with plug-in power

The standard-issue Prius has been mocked.

Poking fun at the Toyota Prius has been a popular pastime. Owners, including movie stars Cameron Diaz and Leonardo DiCaprio, say they are getting nowhere near the claimed fuel consumption.

But the Plug-in Prius is a different beast. It looks just like the standard-issue hybrid, it has the same Prius ingredients - an efficient petrol engine, automatic gearbox, electric motor and additional battery pack.

However, this Plug-in Prius returns in excess of 2.8 litres/100km (100mpg) in petrol-powered mode.

Simon Sheldon, managing director of Amberjac Projects of Grantham, Lincolnshire, which is behind the Plug-in Prius, points to a tray of batteries.

"Those are the original nickel-metal hydride batteries, which we have replaced with lithium-iron phosphate."

These have seven times the capacity of the originals and the cars in which they are fitted get 27 times the energy, says Sheldon.

Plus, they are safe: Sheldon stabs a battery cell right through with a screwdriver without causing a fire. Indeed, the cell still works.

As well as clever batteries there is also a better battery management system, which helps this modified Prius to travel 50km in electric mode (30 times higher than the standard car) and allows it to return up to 2.1 litres/100km compared with 5.6 litres/100km (50mpg) in petrol mode.

"We thought we could do a much better job than Toyota, Sheldon said. "Doubling the car's efficiency seemed achievable. I've worked in the automotive sector and in the battery industry and there is a huge skills gap between the two. One does not realise what the other is doing. That's given us a huge opportunity.

"To get to this customer-ready stage has cost about $431,000," says Sheldon.

At the rear bumper of the Plug-in is a flap which covers a socket. Unlike a standard Prius, you boost the batteries overnight on cheap-rate electricity (it costs only 63c to fill up), and that is the key to its remarkable urban performance.

Engage the gears and you are off at a whisper, powered by the electric motor. You can have climate control and soothing music without flattening the batteries.

There is a pod in front of the driver. "Our monitor shows you the battery condition and the throttle position," says Sheldon.

In addition, there is the Toyota's own colourful and mesmeric energy monitor, which tells you what the power units are doing.

After a few minutes in a standard Prius, the engine cuts in to help the batteries, but the Plug-in just keeps on going, and will travel under pure battery power for 50km.

"We have had a problem describing what this car is," says Sheldon. "It isn't strictly a hybrid, or purely an electric. It is in between.

"We still have to warm up the engine, and for that we do need to burn some petrol so that the catalyser works efficiently.

"We accelerate to more than 50km/h and the petrol engine kicks in. At 100km/h (60mph) we are doing 2.8 litres/100km (100mpg).

And when you coast up to roundabouts, you are only on battery power.

So why do standard Prius owners say they are not getting the same fuel consumption results as Toyota?

"Their driving style needs to change," says Sheldon. "You need to anticipate conditions - there is no point in accelerating hard halfway up a hill.

"Toyota claims 65mpg (4.3 litres/100km) but we have found that under normal driving conditions it is more like 48mpg (5.8 litres/100km)."

Unofficially, Toyota has seen the Plug-in conversion and could not believe that someone had reverse-engineered its baby so successfully.

Amberjac can now turn its attention to the hybrid off-road Lexus RX400h, which gets Sheldon excited: "At just over 30mpg ( 9.4 litres/100km) it doesn't make sense, but we can easily double that figure and I believe it will look much more attractive."

Turn up at Amberjac with your Prius, and for $22,000 plus tax you will have one of the most environmentally friendly cars in the world.

The hardware can all be removed and transferred to your next Prius. Amberjac is also introducing lower-powered battery packs for drivers who don't need to go 50km without an engine, and these versions will cost several thousand dollars less.

Later this year, Amberjac will switch the fuel to bio-ethanol.

- INDEPENDENT