The cells are not 5.2 kWh. In a Model 3 there are thousands of 2170-size cells (less than 5 Ah @ 3.7 V or less than 19 Wh or 0.02 kWh each), grouped in four modules. 5.2 kWh sounds like the energy capacity of an original-style Model S or Model X module (one of 14 or 16 in the Model S/X battery), which contains a few hundred smaller (18650-size) cells.
Something like 50 kWh with a nominal voltage of 350 V is correct so the four modules are about 12 kWh each. (thanks to remy_martian for catching my typo)
Terminology note:
Tesla uses cylindrical cells, roughly like an old-fashioned AA, C, or D flashlight cell. The size designations are just the diameter and length, in millimetres, mashed together...
- 18650: 18 mm diameter by 65.0 mm long (used in most Model S and Model X; about 3 Ah capacity)
- 2170: 21 mm diameter by 70 mm long (used in most Model 3 and Model Y; about 5 Ah capacity)
- 4680: 46 mm diameter by 80 mm long (used in some of the newest Model Y; about 9 Ah capacity)
