Jetcat doesn't use A123 packs (in the UK at least). They use LifePo4.

It's already been stated what the plug is - it's a JST EH (which FMA call the KO).

The link that I posted above shows what you need. It is a new board. You could probably get a cable from somewhere (or make one) but the boards are cheap and if you ever get a pack with a different number of serial cells you won't need to buy another cable.