Just some clarifications to the previous post from larsco2002.
I have three Mamiya 645 bodies - two "Super", and one "Pro".
The other advantage of the Pro Tl over the Pro is that it is likely to be newer, because it replaced the Pro in the line. Otherwise, the only functional difference as far as I am aware is that it offers Ttl flash capability.
The AF models have entirely different designations - there is no "Pro" in that line.
Here is a link to the page on the Mamiya USA website where downloadable manuals can be obtained:
http://www.mamiya.com/customer-service-instruction-manuals-downloads-645.html
They should answer the questions about the lithium batteries.
All the manual focus lenses work on all the cameras, but using them on the AF models is less convenient, particularly when using the meters in those cameras.
All the inserts for the manual focus bodies fit every body. The Super, the Pro and the Pro Tl all offer interchangeable backs, while the earlier bodies don't.
The backs for the AF cameras are not interchangeable with the manual focus backs, nor are the AF inserts interchangeable with the manual focus inserts.
Amongst the manual focus backs, there are none that are strictly 120 or strictly 220 backs - all the manual focus backs can take both 120 or 220 inserts, and therefore the medium format film length is determined by the insert, not the back (hint - if you want to pay less for a used back, with insert, buy one with a 220 insert).
The backs evolved slightly from the first Super backs to the Pro Tl backs - they are all compatible, but some find the newer backs to be better.
There are some accessories that aren't interchangeable between the Super and the Pro/Pro Tl, and it can be hard to identify which they are. I've only run into this directly when trying to get a left hand grip for my second Super body - I ended up with the connector that only works on the Pro body, and as a result had to buy one of those

.
As to the reason to choose a Pro over a Super - age is one concern, but the other that I have heard more frequently is that the gearing is supposedly more robust in the Pro, and therefore less likely to fail, especially iif used with a power winder.
There is also a 645E which does not offer interchangeable backs or finders, but does offer a manual Rapid winder.
Hope this helps.
Matt