Reserve battery

Come to think of it, how likely is it that I'll be allowed to take a spare battery on board of an airplane? After all, I cannot immediately prove that the battery is genuine. It might be a bomb in diguise, no? I would have to turn my laptop on and off, with both batteries before officials might believe the truth: I am simply carrying a real spare battery. Still, there is no way I'm leaving my €129 battery behind.