While some leading teams, including Red Bull and Lotus, are struggling to get significant track time, Button managed to complete a race simulation on the third day of testing at Sakhir on Friday.
McLaren has covered 230 laps in Bahrain, more than double what world champion Red Bull has managed.
Bahrain test day three report
While Button admits his team does not have the faster car at the moment, he believes its reliability is a very positive sign ahead of the first race.
"We know we are not the quickest. We know we are not slow either, and the great thing is that we have a lot of laps under our belt," said Button when asked about the car's pace by AUTOSPORT.
"We can do a race distance. That is promising and I think it just shows how tough last year was for us.
"The guys have done a fantastic job. They guys are so pumped for this year, after such a bad year. It's good to see the buzz is back at McLaren."
Bahrain F1 test in pictures
Completing a race distance allowed Button to learn about the challenges drivers will face with fuel economy this year, with only 100kg of fuel allowed in the car.
The 2009 world champion conceded it will not be easy to manage fuel in an efficient way once the racing begins.
"In testing it's relatively easy to do because you just drive around really slow," Button said. "I think we are all going to find it tricky.
"There's a lot of finetuning that's needed for everyone.
"I think for most people it's about being able to get the car to run for a race distance, that's the biggest issue."