Barrett said there was plenty of hunger and drive in the group preparing to play Namibia in Toulouse on Saturday (NZT).
The pre-tournament warm-up loss to South Africa hurt because they were not up to the mark, were off physically and were out-powered by the Springboks.
"On Friday night [against France], particularly around the scrum, there were a few little games being played, but we've got to adapt. There is plenty of fuel in the tank. This group wants to keep getting better. There is no lack of drive off the back of that loss."
The late-summer conditions in which the tournament has started have required some adaptation, especially around the halt in the flow of games for water breaks in the middle of each half.
"They are probably needed from a welfare thing. You can't make excuses if its hot, it's wet, it's cold, whatever, you just roll your sleeves up."
He didn't play against Namibia in the 2019 World Cup, but he knew from those who did play that they would be physical and aggressive, and that was what they were preparing for.
Crusaders teammate Ethan Blackadder would bring plenty of energy after his call-up as a replacement for wing Emoni Narawa.
"He's got an engine that just keeps chugging, like a diesel. That's what he brings, and the boys love what he does."
Second five-eighths Jordie Barrett said his injured knee was improving.
"It's coming along pretty good. [It's been] a slow 10-14 days, but it's on the improve. So, just day-by-day. It's a funny one. It's come on out of nowhere in the past couple of weeks. [It was] just a joint injury and a bit of inflammation, but I am getting there and making progress each day.
"I got through today really well which is positive and got through some running. I didn't do any running last week at all, just been on the watt bike."
He said the first-game loss to France was not the end of the tournament.
"You only need to look at what happened four years ago. South Africa were world champs, and they lost the first game and got a few lessons in that game that put them in great stead for the rest of the tournament, and we're looking to do something similar.
"It's hot here at the moment, and we probably didn't adapt to those conditions as well as we could have last weekend. We've seen teams in the last few days do that as well. Teams without the ball are going a long way to winning some of these Test matches, kicking a lot, and forcing many mistakes. It's so hard to hold the ball.
"George Ford (England's first five-eighths) kicked 27 points with 14 men on the park, and he was outstanding, and the Welsh made over 200 tackles, and an attacking side like Fiji couldn't cross until the last quarter just because it's so greasy.
"We found in our game there was only 27 minutes of ball in play, which was pretty crazy. In a match, we would like that number to be higher and bring some fatigue into the game and potentially reduce those water breaks so we can use that to our advantage more."
All Blacks v Namibia: Saturday 16 September, 7am NZT (Friday 15 September, 9pm CEST). Live on Sky Sport.