Nice technology, but the price has to be related to its usefulness.
Well, try as I might, I cannot replicate the shutter problem on the RZ with the back off and looking through the lens. It seems perfectly steady. Could the electrical contacts on the back have anything to do with this? I have no idea what those do other than maybe sync up with a metered prism, which I don't have.
Really off topic: lots of uses around the house for it too. Stuff like the batteries in remote controls. I was also using mine recently to see if the rechargeable batteries for the outdoor solar powered garden lights were still any good. (A lot of them weren't.)
And Parker--the easy answer is to get four new ones, stick them in the tester, test the old batteries, and if they're still good pop 'em right back in. ;) On the RZ--any chance something metallic (non metered prism?) is making contact on the camera body where the AE viewfinder terminals are? Mine has a little plastic insert to cover those terminals up. Black electrical tape could work too. The contacts on the film backs are only for setting the film speed for the metered prisms. They shouldn't be doing anything to the shutter.
Lithium batteries are a bit more robust in cold conditions than either alkaline or zinc. In New Zealand I was shooting in temperatures of 3°C often, cold enough to impair my dexterity and fog optics.
It's a very different camera, but of notable mention: my EOS1N's power drive booster E1 holds 8 lithium AA batteries (for reducing weight and readiness in cold and hot conditions). This set will have been in service for 7 years this June (!)
I have no idea how many rolls/exposures over that time. Lithium batteries have a steep 'sudden death' curve, manifesting as hesitation, then an unpredictable 'stop': in some cameras this can mean a film jam/inability to rewind/mirror lock/shutter lock or a combination of them. They really need to be tested every couple of months to observe any 'creep' leading to failure.