Thanks beto-pty, I'll keep that in mind if I decide to add mechanical brakes
I took the board out for a little spin but ended up having to walk back 2 miles because I forgot to charge my batteries! Nevertheless, the board was great fun and if anyone is looking for a 6s ESC, I can recommend the Toro 150A.
So I've sorted out the wiring now (I think) and should be able to charge/ride without removing anything. The 3 x 3s batteries will be charged in parallel whilst in situ.
I have made a little panel mount for the plugs. It's messy and I'll probably re-make it for the final housing but while I ride the board for reliability testing it will do. The panel has 4 x XT60 connectors and 1 x 3s JST balance plug:
These connections are bridged with three XT60 'loop keys'. Each plug breaks/connects the circuit after each 3s pack. When they are plugged in, the circuit is complete and the board is ready to ride:
When charging, the three plugs above are removed, taking the batteries out of series. The pos/neg from the charger is connected to the fourth XT60 connector and they are now connected in parallel. Plug in the balance lead and they are ready to charge. The charger will see them as a 24Ah 3s battery (3 x 8Ah 3s):
This is the wiring which will live inside the housing. It makes my cry looking at this, I have to have had my coffee before I even think about trying to remember which bit plugs into what :| :
It's definitely not an elegant solution but I shouldn't need to remove my batteries to charge them and I don't need to buy an expensive charger. Let's hope my soldering is up to scratch, we'll find out at the weekend when I test it again.