The charger port pins are electric terminals so anything used to clean terminals would work. Unless you already have a can of terminal cleaner then I would not invest in one and recommend using WD40 or another similar product that you already have instead.
Since the charger port terminals are live and energized with electricity nothing with metal should be used to clean them unless the battery pack is unplugged first. Very fine grade sandpaper or green plastic scouring pad would be a good choice for cleaning the pins and these products are non-metallic.
If the charger port terminals have rusted then the plating on them has been corroded though and they will be prone to rust again as soon as they are subjected to moisture or water again. If you have to invest anything into cleaners then it might be a better value to purchase a new charger port instead.
The Razor Crazy Cart's power switch makes a gentle click sound when it is switched on or off. This clicking sound gets quieter the more the switch is used though.