Good luck and the number(s) are HIGHLY variable. I have had my Roadster for 7.5 years and have had no issues keeping it running. Early while under warranty the accelerator pedal was throwing errors causing the car to shut down. The Rangers did a great job and solved the issue by replacing the rear wiring harness under warranty. Then out of warranty the high voltage controller went out and was a $1100 repair. So not crazy but it did have to go to the service center. One other issue was the TPMS sensors needed repaired. We should be able to do that ourselves. And I have learned we can do that on the 1.5 Roadsters. I have started to do all my other maintenance. Fortunately there is a great group here and I have great hope we will keep these cars on the road.
In buying one it depends on what you are looking for. If you do not have plans to get the 3.0 battery then you want to check the ideal miles on a standard charge. More is better, 185 miles is basically a new battery. Mine after 9.5 years and 44,500 miles charges to 166 miles. I would look at Tom's owners battery study for all the details.
Battery Survey « Plug In America