All the experts that I have come across all seem to agree that you get optimum battery performance if you stick between the limits of approx. 20% and 80%, meaning that the range is already effectively reduced to just 60% of whatever fanciful claims they were making in the brochure. That translates into the need to plan at least one charging stop on longish trips, each way, thus adding to both cost and time taken to do the trip, and that is without the extra time required to maximise the range by attempting to sit in the slipstream of buses or trucks at speeds in the 50 to 55 mph range. Allowing a battery to get ultra low can considerably shorten its life expectancy, and the same is equally true if allowing it to charge above an 80% SOC level. Now if you're the driver of a company car and you know that you're going to be getting another new replacement car at the 3 year period, then all the above means bugger all to you as it is never going to come back to bite your arse; it becomes someone else's problem when the battery fails, needing £thousands to replace it with a new one. Even my brand new mobile phone has an upper limit built in of 80% SOC and switches off the charging once this level is reached. When battery gets into the lower regions of below 20%, it goes into low power mode and starts to shut down some services to conserve the battery. Indeed my also brand new laptop also has the same battery management control built in, and it will not go above the 80% level, regardless of how long I leave it on charge, and it also shuts down featured when it gets below 20% level. So I would say that by allowing your car to get to that level, you are actually playing with fire which could potentially hit you extremely hard in the trouser pocket department one day. It is also reasonably true of ICE cars by the way, once the low fuel warning light comes on, it is best to refuel ASAP, regardless of the cost as allowing the tank to get really low, also allows the sediment that slowly accumulates in the tank, to get sucked into the engine, where it could cause serious problems. Incidentally, there is zero issue with brimming your fuel tank on an ICE vehicle.