Barca host Champions League opponents Stuttgart tonight with the aggregate locked at 1-1.
"If you're not at 200%, you're out," Alves said. "We have to charge our batteries and be prepared. I want to go through to the next round.
"We have a magnificent opportunity in front of our own fans and in our own stadium. We mustn't waste it.
"We know how important and difficult the competition is. The slightest slip and they can send you home.
"It's a really difficult match and we have to go flat out."