When it comes down to an analysis of cost per kg in the context of weight savings, anyone that owns a 911 GT3 RS will already be familiar with the kind of post-purchase rationalisation involved. Carbon fibre, lightweight alloys and plexiglass windows are standard fare for Porsche’s most lightweight models.

But for those who remain unsatisfied, Porsche have now released a new innovation that will shave a full 10 kg off the weight a 911 GT3, 911 GT3 RS, or Boxster Spyder. Available from January 2010 Porsche is the first car maker in the world to offer a starter battery based on lithium-ion technology.

Weighing less than 6 kg or 13 lb, the new battery is more than 10 kg or 22 lb lighter than a conventional 60 Ah lead battery. But there’s a catch…

Lithium-ion batteries have certain limitations that make them unsuitable at temperatures below 0o C (32o F), so customers who choose this option will be provided with a regular conventional starter battery as well.

The second catch is the price of this upgrade, Euro 1,904 (including 19 per cent VAT in Germany) if specified on a new car or Euro 2,499 if retrofitted after delivery. You might consider that a little pricey for something that could perhaps malfunction if the weather becomes chilly..

The primary reason for developing and introducing the new battery was its lower weight. In cars such as the two versions of the 911 GT3 and the Boxster Spyder, less weight naturally means greater agility and driving dynamics.

In its length and width the lithium-ion battery comes in the same dimensions as the regular battery, but is approximately 70 millimetres or 2.8” lower. The fastening points, electrical connections and voltage range are fully compatible with the respective models, allowing simple and quick replacement of the standard lead battery by the lightweight unit, for example when driving on the track.

It’s advantage though is not just in its lighter weight, in a conventional car battery sometimes only about 30 per cent of the total capacity is actually available for practical use due to the configuration of the system, whereas the lithium-ion battery makes 100% available providing its full power, for example, when starting the engine almost independently of the current charge level. This new lithium-ion technology also enables many more charging and discharging cycles, extending battery life and is also quicker to recharge.

Charging is undertaken using a conventional battery charger, although no word was available at launch as to whether these new lithium-ion batteries can be left plugged in over extended periods using a trickle-charger.

Porsche’s Lithium-Ion starter battery is available to order on cars built from January 2010, or via the Porsche Tequipment catalogue from February 2010.