About tapping 24v out of the battery?
It's never a good solution to do that to cells in series.
Now, I do not know the Magic pie with the internal controller as well as I do the standard motor with external controller, but I understand it's the same controller. The external controller have a thin wire which needs battery power to make the controller operate. On the external controller, this can (should) be used as power on/off control. (that wire should be underneath that white hotglue just right to your phase wires... I can find out which one later...)
If the internal controller have the same option, one should use that one instead of breaking the main power. The reason for a failing key-switch when operating directly on the main power cables, are actually those condensators you just soldered.
Each time you turn on the power, those condensators charge quickly, making a huge spark inside the key-switch.
Using the thin control-power wire instead, those condensators will always be charged, and sparks (and wear) are avoided.
When the controller are turned 'off' with that control-wire, the controller uses 2-3mA, so the drain on the battery are neglible.
Besides, it gives one the opportunity to utilitize the anti-theft alarm...
Edit:
Regarding the capacitors;
you should dab a little hot-glue around the bases of those caps, to prevent them from vibrating and come loose again.
