Could someone please tell me if I can use Metz 60ct-1 battery pack for Metz 60ct-4 interchangeably? Also can I use two 60ct-4 heads with one battery pack? I have two 60ct-4 heads and one battery pack. There are 2 connectors on the battery pack for connecting the head, but I am not sure to plug in 2 heads into it. Any input is greatly appreciated.