Universal Cable, when the source is an IC2 energy storage, seem to always send out the full packet size, even if less is needed.
I did some extensive testing and here are my results.
The setup is IC2 energy storage -> Universal Cable -> Pulverizer (from TE).
First method: I let the Pulverizer and the MFSU fully charge and disconnect the cabling
Now I pulverize one Iron Ore, which uses 4000 RF
I connect the cables again, there are reproducably 1.880 EU missing in the MFSU
I charge the MFSU again and keep the Pulverizer connected
I pulverize one Iron Ore again
Now the MFSU is missing 102.232 EU
I repeat the test with an MFE:
With the first method, the MFE is only missing 1.024 EU
With the second method, it's missing 25.600 EU
I repeat the tests with a BatBox:
With the first method, it's only missing 800 EU
With the second method, it's missing 1.376 EU
So you can see, it uses less power if the packets that are sent out are smaller
Now, same testing method, but different setup: MFSU -> Universal Cable -> Macerator
Macerating one Iron Ore costs 800 EU
However, with the first method, the MFSU is missing 2048 EU.
With the second method, a whopping 409.600 EU.
Here you can see some screenshots of the setup. The screenshots were taken after the second method. http://imgur.com/a/SZAY9
This is an IC2 bug. Will be fixed as soon as Player gets around to it.