You should buy Alkaline long life types. We do not recommend using rechargeable batteries, as they have limited life and tend to drop voltage very suddenly. We can supply Duracell Procell batteries, which we find last the longest - about 6 hours each.
If you are trying to work out your battery usage, we generally use a set for 2 shows, and a set each for the dress rehearsal and technical. So the formula is:-