Technically, a P2D can't use a AA cell. So, as mattlee suggested, I'm assuming your bought the combo pack with an L1D and a P2D body. Using a rechargeable AA, you're probably at around 1.2v. The CR123's are over 3.0v. Therefore, when using a single AA, there's too little voltage to make the turbo visibly brighter than the high mode. Throw a CR123 in the other body and it should like up! Conversely, using a rechargeable li-ion cell, the voltage is 3.7-4.2v. This voltage is high enough that every mode looks like Turbo.