ZenUtils allow ContentTweaker to add item with RF!

You'd better import the package to avoid errors and write script easier.

import mods.zenutils.cotx.EnergyItem;

You can simply use VanillaFactory.

VanillaFactory.createEnergyItem(String unlocalizedName, int capacity, int maxReceive, int maxExtract)

EnergyItem extends ExpandItem. That means all Methods and ZenProperties that are available for Items are also available for energy items!

It doesn't have special ZenProperties own.