The NJB3 will only accept up to 5 volts DC. any more than that and it won't operate at all. A sony 6v yellow plug will fit, but the voltage is the key, so don't bother with a sony adapter unless you are just cutting the plug off to make a DIY adapter. I haven't tried to do a battery setup, I've just relied on my 2 internnal batteries so far.
One of the problems with using external power is that it charges the battery as it operates, and there is a problem with the unit that makes it lock up when the charging cycle is complete, requiring a reboot of the device. So needless to say, I haven't tried external battery power.
I would suggest a 12v SLA and the auto adapter if you really need more than 5 hrs continuous recording. Otherwise, order extra internal batteries and charge them before the show. Don't forget you can charge 2 at a time.