-- Find all of our peripherals
battery = peripheral.wrap("bottom")

-- Check if we have a battery
if battery == nil then
  error("ER: No battery connected to computer")
end

while true do

  local maxEnergy = matrix.getMaxEnergy()/2.5
  local currEnergy = matrix.getEnergy()/2.5

  battery.getEnergy()

  if currEnergy / maxEnergy < 0.5 then
    redstone.setAnalogOutput("back", 15)
  end
  os.sleep(2)

end