That is Probably EXT. power,As long as you re wire your Battery Boxes and keep the voltage below 4 volts ...you are good.
Your camera will pull off these EXT. Bat. for some time
You have to wire in Parallel,you can put 4 0r even 8 D Battery;s together as long as the you have POS. to Pos and Neg. to Neg.
If you wire them in series like they come ...6 volts you will fry your camera.
One more thing..a AA has 1.5 volts and a D has 1.5 volts,
But 4 D;s will last twice as long as 4 AA;s
It has to do with stored energy,I think the word I am hunting is amps.
I wired ....just for the heck of it 4 D;s to put out 1.5 volts...My cam would not even power up...I had it so low it began pulling from my cam,electricity will take the easiest route ...much like light.
But If he was putting in a Slave Flash... that may be the reason for the EXT.....FIREMAN JIM can tell you about them.
I myself think they are a waste ,you can Download software to brighten a Photo to make it look like it is daylight.
If you do not believe me go to Outdoor Talk and look at Bob R
post about the Sony program ...I think it is PMB.
It is incredible at what it will do ...in one photo you cannot see the bear ...when he apply;s his software it looks like daytime,and not all washed out.
