Energycell Reader

A very simple program, Not sure if it's what you wanted. You do require the newest version of openPeripheral for this to work.
redstoneSide = "right" -- Where to output redstone signal
redstoneState = true -- What state to put the redstone in when the chosen limit hits
energyPercent = 90 -- what percentage to react on
reCheckTimer = 5 -- How many seconds to wait before it checks again
EnergyCellSide = "left" -- Which side of the computer the energy cell is on

enCell = peripheral.wrap(EnergyCellSide)

function getEnergy()
    return enCell.getEnergyStored("unknown")
end

function getMaxEnergy()
    return enCell.getMaxEnergyStored("unkown")
end

function getEnergyPercent()
    return math.floor(getEnergy()/getMaxEnergy()*100)
end

while true do
    if getEnergyPercent() >= energyPercent then
        rs.setOutput(redstoneSide, redstoneState)
    else
        rs.setOutput(redstoneSide, not redstoneState)
    end
    sleep(reCheckTimer)
end