Just lie to me and tell me the worst case scenario. If the customer focused lie puts you in a marketing bind because the truth is you can't meet what you're alleging to sell... That's your problem. As a customer, I don't need the anxiety of estimations being off by almost 100%. What use is that for me? It's only use is to minimally meet your marketing book of lies to sell technology that isn't quite there yet and put the onus, expense, and anxiety of this transition onto the customer.

Put it this way, I've never ended a journey and been annoyed I had more miles left in the tank than it promised. But you can bet the opposite would have be stranded and screaming on a highway somewhere instead. Why do you want your customers to retain that angst against your brand? Cars of all things are long term, emotional investments. Screwing one customer and they don't stay quiet.

Either way, we're car beta testers now.