Here's a "feature" of the plain 645: there's no battery power indicator. Seems you know your AA's are running low when the film transport starts to malfunction.
Guess what happened to me this morning.
Here I was: brand spankin' new *awesome* A 55mm lens from Hinman mounted, I drive an extra 20 minutes out of my way to get to a meadow, snow covered, fall foliaged, mist rising, sun rising... and kerplunk. Film stops advancing.
At work I waste the roll opening the back to see if there's anything amiss. I believe it's the batteries finally going low.
Bah.
Which model of 645 started to include a battery indicator?