Another cool method of storing power at truly insane densities would be a DSU full of bedrockium drums of hot CO2 from ReactorCraft. Much like fish, you then have to convert the hot CO2 into energy with the appropriate setup but (2^31) * 65,536,000 mB of Hot CO2 running through a nicely efficient boiler/turbine setup will make a monumental amount of power.
https://forum.feed-the-beast.com/th...-of-big-reactors-and-tesseracts.109476/page-2
EDIT: I did the math a while back and one DSU of bedrockium drums of hot CO2 should yield around 200,000,000,000,000,000,000,000 RF using an efficient setup.