Button finished second quickest on the second day of the final test at Barcelona's Circuit de Catalunya which again was blighted by early rain and cold temperatures.
That was evident in the times as Button's best lap of his 72 was one minute 23.181secs, 0.465s adrift of Lotus' Romain Grosjean who was on the faster softer Pirelli tyre compared to the Briton on the medium compound.
The Frenchman's time was still a second off the quickest at the track so far, set by Button's team-mate Sergio Perez when the temperatures were at their highest in the middle of last week.
Button, though, was much happier Friday compared to a week ago as he said: "For us, it's been the best day we've had in testing, with the feeling of the car and more of an understanding with it now.
"At the last test I said we didn't really understand the car - amazing how negative that was taken by a lot of people.
"But it's what testing is all about, learning from what you do and we have a much better understanding now, although we're still not quite there in terms of pace."
This weekend the sun is expected to shine and temperatures expected to rise to 16 degrees centigrade, which should help all of the teams.
"We should have good weather, so a very important two days for us before Melbourne," added Button, who is back in the car for the final day of testing on Sunday.
"It will be nice to test with a bit of temperature. It's been a while since it's been warm, and I've not driven around Barcelona in hot conditions yet, so I'm looking forward to that.
"Hopefully we will have two dry days which need to be 100-lap days at least, and we can get a much better read on where we stand.
"For ourselves, we need a bit of confidence going into the first race in Melbourne."
Half a second behind Button was Williams' Pastor Maldonado, followed by triple world champion Sebastian Vettel who has yet to top the timesheet in his Red Bull.
Like team-mate Mark Webber Thursday, Vettel does not believe the team will run away with it in Melbourne on March 17.
"It's very difficult to know where we are in terms of pace," said Vettel.
"We have a rough idea, and everything is fine. We're happy with the balance, how the car behaves, which is the positive for us.
"Whether that's enough for us, we don't know at this stage, and of course conditions now are very different from what we'll see in Melbourne.
"I don't think it will be a surprise if someone deals better with the conditions there."
Sauber's Nico Hulkenberg was fifth fastest ahead of Adrian Sutil in his first official day back in the car for Force India after he was confirmed as their second driver for this season only yesterday.
Toro Rosso's Daniel Ricciardo and Max Chilton for Marussia were down in seventh and eighth, almost four seconds adrift, followed by the Caterham of Giedo van der Garde.
Surprisingly, at the bottom of the timesheet were Nico Rosberg in his Mercedes and Ferrari's Fernando Alonso, four and five seconds off the pace respectively.
Both drivers completed over 100 laps, albeit with both teams running very different programmes compared to the quickest cars.