World champion Lewis Hamilton is facing a truncated testing schedule in getting to grips with the technical changes Formula One will embrace this season.
McLaren is one of the teams that is using kinetic energy recovery systems - one of the many changes that are being introduced for 2009 - in its two cars.
"I've seven days to master the car, where normally I would have had 20 days," Hamilton, 24, told BBC Sport.
"It's a completely new package for us all - it's going to be interesting."
Kers harnesses energy that would have been lost during braking and allows the driver to reapply it during acceleration.
"We've a huge challenge ahead of us with Kers - with the reliability of that, the reliability of the car and finding the new set-up," said Hamilton, who got his first taste of McLaren's 2009 car when he completed 81 laps in testing in Portugal on Wednesday.
I'm pleased to report the car feels good
Hamilton said McLaren would definitely be using the system - other teams have yet to decide whether to employ it or not from the start of the season.
The 24-year-old decided to take more time off at the end of last season after he became the youngest world champion in Formula One history after a thrilling Brazilian Grand Prix.
His team-mate Heikki Kovalainen is still waiting to try out his new McLaren after bad weather wiped out the final day of testing in southern Portugal on Thursday.
The Finn had been due to drive the MP4-24 at the Algarve circuit, but rain and fog grounded the medical helicopter and forced organisers to close the circuit for safety reasons.
McLaren's next test is at the Jerez circuit in southern Spain on 10 February, with the F1 season starting in Australia on 29 March.
Driving for the first time since winning the F1 title in dramatic fashion at the Brazilian Grand Prix, Hamilton was third fastest overall after a minor engine problem.
"It was good to be back working with the team. It felt like I'd hardly been away because it was easy to slip back into the routine," said Hamilton.
"This first test was all about just getting used to the new car and the new regulations and about giving my feedback to the engineers - it wasn't about setting a fast time.
"I'm pleased to report that the car feels good, we've made lots of progress over the winter and I'm looking forward to developing the car ahead of the Australian Grand Prix.
"It's going to be an extremely busy winter. I've only been in the car for one day and our usual job list for the weeks ahead is already enormous.
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