This is what I've found:
def drainEnergy(requested: Double): Double = museEnergyFromEU(ElectricItem.manager.discharge(stack, museEnergyToEU(requested), getTier, true, false, false))
It appears that the external boolean is set to false, meaning any of these items shouldn't be able to provide battery to tools, right?
Further, it seems that he's using ElectricItem and not IElectricItem, which could be a problem. He doesn't provide the .jar for ElectricItem, and the only classes that are instantiated are for IElectricItem.
I'm trying to follow the classes back up to figure out where the disconnect is, but like I said, I'm unfamiliar with modding in general.
EDIT: After finding the API linked by Greg, I'm pretty sure I've determined that the API calls are all correct. If the item calls ElectricItem.manager.discharge() like you say, then the items should recharge from it.
I do note that the power armor traces back up to an overridden version of discharge, implemented in MuseElectricItem, but it looks like that one is kosher, too. I'm not seeing anywhere that there are glaring code errors. Does anyone have another suggestion? Maybe some in-game diagnostics I could do to determine what's happening?