Brandon Flowers is always worried The Killers will be "obsolete."

The 31-year-old singer admits he has found writing the band's fourth album Battle Born to be his toughest yet because he is nervous fans of the group's music will have moved on: "The expectation seems to increase with every album. It doesn't get any easier - you want to earn your keep. It's the hardest thing I've done. I'm always worried that people are going to have moved on, that something will have happened to make us obsolete, but I think we'll be OK. This who thing has happened so fast that's it's always real hard for us to understand."

However, Brandon does admit he has begun taking singing lessons so he can put more strength in his vocals. "Yeah I want to be stronger. I heard that the male voice isn't mature until you're about 33, and I'm almost there, so I thought, 'You might as well exercise this sucker,'" He added to Britain's ELLE.