Power Storage This can hold over 1,000,000 (1 million) units of power, using multiple mods and advanced building (the mod) to make it look smaller.
As a comparison, the GSO battery can hold 1500 units of power.
As a fellow terra tech player, I have a suggestion for a tech to anyone who might read this. Using Sozin's 40k block pack, it is possible to make gigantic warships that don't have batteries but are instead using 100% generators, the basis for my newest project, the Indestructible line of heavy cruisers for nova. I think it would be a fun challenge to see how they might work for you. They could easily make ships undefeatable unless using shield piercing munitions. I might post a test version of one that I have been building.