First off, I should say that I prefer German Engineering and Optics.. secondly, I would like to admit that mostly all German stuff is overpriced and/or rather expensive. I have recently purchased 2 ETRSi bodies, a motor drive, a speed grip, a regular prism and a metered prism, 2x120 backs, 1x220 back, a 150mm, a 50mm and 2x 75mm lenses for less than $400 (2 separate purchases) and I attribute my success to the 6.2 volt Silver Oxide battery. So here is how it happened. The ETRSi and the Pentax 6x7 share a common feature. The shutter is operated by the 6.2 volt power source. Without the battery, the ETRSi will only fire at 1/500th of a second and the Pentax, well.. without a battery, it just will not work. The solution? Buy extra batteries.. the silver oxide has a 7+year shelf life and are fairly cheap when bought in bulk (I bought 20 for about $50) although with the early Pentax (the 6x7, not the 67) there is a bypass trick.. you can jury rig (4xaa=6v) a remote energy source for your time exposures as the 6x7 uses juice all through the exposure and is the reason for constant battery failure. Anyway, about the 645.. both cameras had battery issues. One had a new battery but the motor drive (uses 6xAA) had a design flaw. The battery contact is a rivet that can go bad if the unattended power pack is left loaded in storage. The corrosion between the rivet and the metal strap kept the contacts from.. well contacting. Took me about 10 minutes to fix it by stripping a piece of copper wire and following the pathway to assure contact. I purchased this camera with a Pentax 6x7 which in addition to being a pain to cock and fire, it also had a bad battery. The second ETRSi I bought simply had a bad 6volt battery which also had the effect of not being able to cock and fire the shutter.
So the point? Check the battery. Many people just give up, sell or trade and I am the benificiary of their impatience.
Ahhhh... my first post!