zzounds.com has them new for $49. i would guess depending on your mic load, that at a load of 4ma i would say that with the 2 9v's. they might last bout 20 hrs... thats a guess. i have a phantom box and the manual says it lasts 50 hrs on 2 9v's at 4ma, but i'm taking into account 2 mics.. so cut that in half... yea.. thats what i got.. i'd say go for it.. cheap way to power mics.. good luck.. peace.