Using a non apple cheap car charger

My question is this. I have heard that using cheap iphone charger (not the just cable but the actual charger) can damage and/or shorten the battery life span. By cheap I mean from a gas station cheap. I understand the usage of the amp and voltage. My boss tells us to go to the gas station to buy a car charger for our work trucks. I need confirmation if this is true or not. If true then I need Apple's stating this or a third party stating it.