Let's say right up front that we don't know for sure if Nissan's 100 mile range estimate for its new LEAF electric car is overly optimistic or not. No one outside of Nissan has actually tested the car to verify it one way or the other. However, based on what we do know, it's not unreasonable to expect the range to fall short of 100 miles in real world use.
Ex-Tesla SVP Marketing Darryl Siry has real world knowledge of the correlation between the EPA city range estimate that Nissan is quoting and reality. He has previously penned missives on the dangers of EV makers over-selling and under-delivering on range and his warning still holds true.
It's certainly possible that Nissan has created a particularly efficient EV that can actually get 100 miles per charge in normal, everyday use. At this point, we don't know much about Nissan's control strategy for the car and the battery. Based on what we do know, there is good reason to be skeptical. The LEAF's 24 kWh battery pack is considerably smaller than the 35 kWh pack in the MINI E, a small car that struggles to get 100 miles. Of course, the MINI is far from optimized. The Tesla Roadster gets about 220 miles in similar testing from a 53 kWh pack. Tesla, however, is using almost the full capacity of its pack to get its range and that is expected to yield a shortened lifespan for the pack (approx. five-to-six years). If Nissan follows the same path with the LEAF pack, the type of customers it is aiming for will not be pleased with having to replace the pack prematurely. Nissan
Only time will tell what Nissan is really planning on doing. However, as one of the leading proponents of EVs with very high-volume plans in the near term, Nissan should be wary of over-promising.