Electrical Engine GUI Question

[Servillo]

I've got an Electrical Engine that I'm using to power some of the BC and Forestry crafting tools as needed, and I have a question regarding some of the slots on the GUI. I understand what the slot on the far left is for, circuit boards with tubes attached to improve engine performance, but the slots in the middle are a mystery to me. One of them looks like it has a two-bladed fan in it, the other is a completely empty slot, and there's a bar next to it. I cannot find anything that tells me what these are for.

 

[SilvasRuin]

The top one isn't a slot, it IS a fan. Or represents one at least. I'm really not sure what the actual slot on the bottom is for, but people have said something about a IC2 battery to power the fan... I guess it keeps the engine cool for when higher amounts of EU are wired into it? Maybe?

 

[Nemesis688]

The bottom slot is to power the engine with re-battery or an energy crystal. The fan is the symbol for alternating current. Which is just an aesthetic. It's not really a slot.

 

[Servillo]

Ahhh, okay. That makes sense. That's a different symbol for AC current than I'm used to seeing, so that explains why I don't recognize it. Thanks.

 

[LadyBriar]

You can put heat vents in the bottom slot to keep the electrical engines from overheating and shutting down to cool as much. They're AWESOME!