there is another solution: CR 123 batteries, which are 3V, but it's even sufficient to replace the older 4.5 V batteries. there are small, cheap and easy to use holders which fit into the space of the old battery. have a look here what it looks like:
cr 123 batteries last very long. I converted all my polariod pack film cameras to this, a 250, a 430 and two 360 (two batteries each).