[BBC-Micro] Batteries in a Master

[Kris Adcock]

I always thought that you needed three AA batteries inside a Master, but 
  I've just opened one up and there is only space for (at most) two.

Up until now, all the Masters I have opened have had their battery packs 
  hidden under the keyboard, or between motherboard and PSU. But this 
one is wired so that the batteries go in the plastic next to the 
cartridge slots. There's room for two batteries, but the terminals are 
arranged so that the batteries would be in parallel (so the voltage 
would still be 1.5v).

Is this right? Is the supply for the Master supposed to be 1.5v, but 
some Masters chose to use three batteries so they didn't need changing 
as often?

Cheers,

Kris.