Red Bull are thought to have a mini-Kers system they use only at the race start. This allows them to defend their position at the start without some of the disadvantages of a full KERS system.
A fully optimised KERS provides an average performance boost of 0.3 seconds a lap by harvesting energy that would have been wasted during braking, storing it in batteries and then reapplying it during acceleration.
But the system's power is limited by the regulations and the heavy batteries and other parts create packaging and weight distribution problems. Equally, as the system relies on the rear wheels to provide its charge, it can increase tyre wear in races because it unsettles the handling of the car.
That is a potentially key advantage in a year when the new Pirelli tyres have been designed to degrade more quickly than the Bridgestones F1 used in the last few years.
Because of this, some teams believe a car can be made to perform faster without Kers.
Rivals teams believe Red Bull have built a Kers system with a smaller battery which is charged before the race, discharged only once at the start and not used again. The system would still need a fairly large battery to deliver the high current needed but weight could be saved because the parts needed to charge the battery during the race would not be required.
What is not clear is whether this was Red Bull's design from the start or whether they were forced to go down this route because they could not get the full system reliable enough for a race. In theory, taking this approach means the car can be made faster over one lap while ensuring they are not easily passed by those of Kers-equipped rivals close behind. Red Bull would then rely on the inherent pace of their car to keep them clear of the threat of being passed in the race.
However, there is a major risk with Red Bull's approach. If they do find themselves under threat from a Kers-equipped car in a race, Vettel and team-mate Mark Webber would be virtually defenceless.
Team principal Christian Horner would not confirm or deny the presence of the system.
But he said: "All I will tell you is our system is not the same as others' but it's at its most beneficial at the start." Vettel said after qualifying that he had not been using his Kers during the session. Webber added: "We didn't run it today for reasons we will keep in the team."
Rivals were stunned by the pace of the Red Bulls in Australia after pre-season testing had appeared to suggest that they and Ferrari would be evenly matched. Ferrari driver Fernando Alonso, who qualified fifth, said he believed the Italian team had failed to extract the full potential of their car on Saturday.
A leading engineer from another team said he thought it "very likely" that Red Bull had such a system as his team were working on a similar idea themselves.
UPDATE: Red Bull team principal Christian Horner revealed after Sebastian Vettel's season-opening victory in Melbourne that the team did not have KERS on its RB7s from Saturday onwards. "We haven't had KERS on at all this weekend," said Horner.
"We didn't want to tell anybody, but looking at the start ... It didn't look like we needed it. We were a bit nervous about telling everybody before the race. We ran it on Friday and we weren't happy with the reliability, we felt it was a potential risk, so we took it off both cars and didn't race it at all this weekend."