I've come across a couple of games recently that someone has used this style battery holder and just soldered them in and left them hanging by the wires  

The remote battery pack is a good idea but it must be done in a way that it can't short on anything.
I had an instance were a person transported a machine with one of the open style battery packs and when the back box was put up the battery pack hooked on one of the transistors in the display driver HV section. he didn't open the back box before turning it on and     every board required repairs after that.

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.