Serial charging is a little tricky. At best only worthwhile with packs at very similar charge states and capacities. Generally parallel charging is safer and frequently faster. To make best use of either requires a suitably powered charger. What charger do you have?

But here are some diagrams that may help. One balance wire is redundant. Suggest double checking everything with a voltmeter, don't assume!



This is for 3S packs but shows the trend: