MFSU is the largest energy storage block in Industrial Craft 2: the internal battery holds 40 million EU and transfers up to 2,048 EU per tick at power tier 4. The storage ladder reads BatBox (40,000 EU, 32 EU per tick), CESU (300,000 EU, 128), MFE (4,000,000 EU, 512) and MFSU (40,000,000 EU, 2,048) — ten times the charge of an MFE. When placed, the MFSU sends power out through the face marked with a dot — the face aimed at the player — while the other five faces accept incoming cable. Any single input packet above 2,048 EU per tick makes the MFSU explode, so a transformer belongs in front of the block on high-voltage lines. A wrenched-out MFSU keeps only 80% of the stored EU, and even the crafting components hold more charge together (64 million EU).

The MFSU GUI doubles as a charging dock: the top slot charges a held battery or Lapotron Crystal from the internal storage, the bottom slot drains charged items back into the battery, and four armour slots recharge equipped armour without opening the inventory. A button in the GUI corner cycles seven redstone modes, from silent storage to 'do not output energy'. Players who already run an MFE can right-click the placed MFE with an MFSU Upgrade Kit: the MFE converts on the spot and the stored EU carries over, dodging the 80% relocation loss. One MFSU also serves as an ingredient in the Chargepad recipe. For a growing power grid, the MFSU is the buffer that keeps machines fed through demand spikes.