a simple bump of the wall or another car.. will remove anything you do to wires and or connectors...
best TEST.... for motor/controller/battery wires and connectors.. use an infrared temp meter... any heat = loss..
back in the 'Day' each round needed a fresh battery.. now days... one battery for one car... just a quick recharge..if any.
a single round might use 800 to 1,200 mah... so a 4,000mah battery is good..