I’m so sorry to know it seems that nobody mentioned that the energy which a TileEntityBase10EnergyConverter accepted and emitted is defined in NBT data when it registered with gregapi.block.multitileentity.MultiTileEntityRegistry.add(String aLocalised, String aCategoricalName, int aID, int aCreativeTabID, Class<? extends TileEntity> aClass, int aBlockMetaData, int aStackSize, MultiTileEntityBlock aBlock, NBTTagCompound aParameters, Object… aRecipe)
Please Check gregtech.loader.b.Loader_MultiTileEntites.java to get further details about how to use this method.