The larger tanks can hold anything any other tank can.
Large electric: power: 400, battery used: 40000
Massive electric: power: 1000, battery used: 140000
So the massive electric is about 2.5x as powerful for 3.5x the power usage. It is intended for power, not efficiency.
The storage battery array is floor to ceiling solid battery, no movement and no sight through it, but it stores a hell of a lot.