People at the sphere recommend a pre-charge bypass resistor allowing some current slowly through to the controller caps before you switch
I just use one of these. .
Each pole allows 240v 15 amps so I use both centre poles to battery and throw to the controller and on the opposite throw I connect the battery so when I switch off it connects to the charger plug. This has it has never failed me
If I look into the switch really close in the dark I only notice the smallest of sparks. My controller is 40 AMPS.