The animation behind Elon shows 8 modules building up the battery. We know from previous comments that the M3 battery will be smaller, both physically and in capacity, so how are they able to get an EPA of 215 miles out of such a small battery?
Let me start by saying that I am not convinced that the M3 will be 40% lighter than a base S85, or massively more aerodynamic. The curb weight of the S85 was about 2,100kg. The M3 is "20%" smaller, but a lot of the aluminium has been replaced by steel, so IMO it is unlikely the car body is much lighter.
Anyway... the RWD S85 had an EPA of 265 miles. It did this with 16 modules, i.e. 16.5 miles/module (or 5.3kWh/module).
For simplicity, let's assume that the full 85kWh is used (we know it is not).
If the M3 had the same power consumption, it would need 13 "S85" battery modules (69kWh) to get 215 miles, or about 7.5kWh/module. This is far more than the ~5% improvement we saw with the new chemistry used in the 90kWh battery.
So what have they done to reduce power consumption by so much?
One area of improvement which would save weight and energy could be battery cooling - Patent 20150244036 describes a heat pipe system for cooling & heating which I don't remember seeing in a Model S battery, and Patent 20140193683 describes a "battery pack base heat exchanger". Are we seeing some of this tech already in the Powerpack modules...?
Any other ideas how they might have done this (and allowed room for a bigger capacity battery as well!)?