Myimiev and fjpod, when dealing with the intricacies of Lithium Ion battery charging, you need to understand the enormous tradeoffs being made by the design engineers when trying to produce something that is state-of-the-art and yet subject to a heavily-regulated automotive consumer environment - it's amazing to me that major manufacturers are even daring to tread there! Having an 8-year warranty on this product is incredible IMO - and yet very hopeful: look how fantastically the NiMH batteries used in the last decade's hybrids have performed over time!
The major tradeoffs are maximizing battery useful capacity (range) and output power (i.e., vehicle acceleration) vs. battery life, subjected to clueless consumers in a hostile abusive operational environment.
You have to understand that the "battery" is a pack comprised of 100-or-so(?) individual cells in cell subpacks, all of which are individually managed (not simply monitored) for parameters such as voltage, current, temperature, individual cell state-of-charge (SOC) and/or depth-of-discharge (DOD), and then the rate of change for each of these parameters in an attempt to keep the pack's individual cells balanced and protected to maximize the battery pack's life. It's mind-boggling and very proprietary for each manufacturer. If you want to know more about this topic get the book "Battery Management Systems for Large Lithium-Ion Battery Packs" by Davide Andrea.
The battery management system (BMS) is designed to minimize stresses on the battery, and, for conservatism, especially preclude the cell and battery pack excursions into the upper and lower limits (e.g., individual cell open-circuit voltage is but one parameter of concern). Operational limits are well under the maximum limits at each end, which is why the charger undoubtedly stops charging the battery some percentage below its maximum and the BMS first warns and then stops the car at some percentage above the destructive minimum. Over-discharge and over-charge of a Lithium cell can be fatal to the battery, unlike the response of the very abuse-tolerant conventional lead-acid battery.
I wouldn't expect the manufacturer to divulge the amount of conservatism they've put into the operational limits of their BMS, and would be hesitant to associate any specific percentage with what they're doing. For myself, I'm content to operate my iMiEV in a fuel gauge range between two and 14 bars, adding a further level of conservatism which will hopefully result in a long and happy battery life. I have no qualms about fully charging my iMiEV just before a longer trip, and at the bottom end I simply don't want to push its limits for my own personal peace-of-mind.