Here is the series connector used to turn the two 3S3P packs into the 6S3P. These things are very handy to create series packs when you have multiple packs you need to connect. Imagine soldering three, four or five packs to one deans connector? Ouch! These solve the problem and also allow you to charge packs separately at any time.
https://www.fmadirect.com/site/fma.h...roducts&cat=28
they also make parallel connectors. they are same except they put the packs into parallel configuration.
The connectors can be cut to use as many or as few as you need. In this application I needed only 2 so I cut the other 3 off. Once cut I soldered the wires on through the holes and then covered in some electrical tape to insulate any exposed contacts on the connector.