EngineControl

cell = peripheral.wrap("thermalexpansion:storage_cell_0")
capacity = cell.getRFCapacity()

while true do
    if cell.getRFStored() == capacity then
        redstone.setAnalogOutput("left", 0)
    elseif cell.getRFStored() < capacity / 5 then
        redstone.setAnalogOutput("left", 5)
    end
    sleep(20)
end