OK, in this video of the Gigafactory tour at 30:00 the tour guide tells us that each Powerwall consists of a "pod". Each pod consists of 2 modules. A Powerpack consists of 16 pods or 32 modules. He states the module of 14x32 cells is the same form factor that is used in the model S. He later states that there are 16 modules in the Model S.
Some quick calculations:
1 module has 14x32 = 448 cells
A Powerwall has 2 modues = 896 cells
A Model S has 16 modules = 7168 cells
A Powerpack has 32 modules = 14336 cells.
This is the fishy part. A Powerwall is rated 6.4Kwh and a Powerpack is rated 100Kwh. That would mean the batteries used in them would have a capacity of only 2.0ah a piece. This is a very low capacity battery. In fact 2.0ah is very old technology. Not even the Roadster uses such small capacity batteries.
My theory is that since the Powerpack and Powerwall are going to have to endure the same sort of charge/discharge cycles as a Model S, Tesla is actually using the exact same batteries for both their vehicles and their Powerwall products to reduce overall costs of said battery type.
Now if we go off the very latest news that Tesla is about to introduce a 100D version of the Model S, we can suppose that they already have that battery in stock and are actually using said battery in their current 90D vehicles. This battery would have a 4.0ah rating.
If that is the case, and they are in fact using the same batteries for all of their operations, then the Powerwall would have an actual rating of 12.8Kwh and the Powerpack would have a nice round rating of 200Kwh.
I might be right or I might be wrong, but you have to agree that Tesla using a 2.0ah rated battery for anything is pretty unlikely.