I have started using the Button style batteries but the only worry i have with that is that the customer has to carry AA batteries and lithium button batteries if they have multiple machines and i am not sure on how long the Button style batteries will last. I know GTB use them in their system 3 CPU boards but they are a larger style cell.
I have a system 11 and 6 wms machines with them fitted and will see how long they last as a test.

From my experience in the computer industry with BIOS batteries (lithium button) I would be surprised if you didn't get a good 7 to 10 years out of them.