Just last night I was browsing through the Cables forum and I came across a post where somebody had gotten some battery stand-ins and had hacked an RC connector to let him connect RC batteries through it to power a 7xx of some kind. I can't find it at the moment, but I'm guess that was getting him above 7.2 volts. I recall it being from at least 4 or 5 years ago.
I was thinking he might have made some comments about voltage ranges but I don't recall for sure, thus I was looking for it.
Thanks Ultfris101. Yeah, after getting the 744 recently, I made myself one of these 'dummy cells' for the back of my 744. I did same thing when I had a 702 a few years ago. What I did was I bought a cheap li-ion battery pack off ebay for like $12 and cut it open. Then I pulled out the guts leaving just the shell and the contacts. Soldered it up with wires to the dummy cells terminals and epoxied the wires so there would be some stress relief. Finally glued the shell back together. On the other end of the wire, I installed a Tamiya connector, which is the connector that Remote Control car batteries use.
So now I can use 7.2V RC car batteries now to power my 744 through this dummy cell as an option to the expensive Sony L style Li-Ion batteries, which of couse are also 7.2V. The reason I was asking about other voltages is I also have a bunch of high cacapacity SLA batteries that would power my 744 all day at a festival. So, I was wondering if I could put a different voltage on these battery terminals than 7.2V. I haven't got that answer yet. Might inquire directly with Sound Devices.
I know that I can buy a hirose connector and do this through the external battery conector though, but I was just trying to avoid spending $50 on another cable if possilble. I know for sure that the 744 will take anywhere from 10 to 18V through that connector. Probably should just break down and do that anyway...would be a nice cable to have.