PC Terminal on Ext Battery Pack?

[MOREGONE]

Hello,

I just got an external battery pack for my Nikon speedlights and am confused why there is a PC socket in addition to the battery plug.

Here is an example of a product on Amazon that looks the same

Amazon.com : Cowboystudio Battery Pack for Nikon Speedlights SB-800, SB-80DX, SB-11, SB-20, SB-22, SB-24 to 28 and SB-28DX : Digital Camera Batteries : Camera & Photo

Doesn't seem to make a difference in whether plugged in or not.
Thanks

 

[Braineack]

looks like a great way to short out a flash...

 

[Vtec44]

I have a similiar battery pack and I think it has to do with high speed sync or something like that. I don't remember exactly.

 

[photoguy99]

SD-8A on a Nikon SB-900 - Photo.net Nikon Forum