local batterySide = "left"
local generatorSide = "bottom"

-- both 0.0 - 1.0
local lowPercent = 0.1
local highPercent = 0.9


local batt = peripheral.wrap(batterySide)

term.clear()

local percentage = nil
local delta = nil
local tempTime = nil
local prevTime = os.epoch("utc")
local prevVal = 0
while true do
    tempTime = os.epoch("utc")
    percentage = batt.getEnergyFilledPercentage()
    delta = percentage - prevVal
    prevVal = percentage

    term.setCursorPos(1,1)
    print(string.format("battery level: %05.2f%%", percentage*100))
    print(string.format("delta: %+06.2f%% / %05.3fs", delta*100, (tempTime-prevTime)/1000))
    prevTime = tempTime

    if percentage < lowPercent then
        redstone.setOutput(generatorSide, true)
    elseif percentage > highPercent then
        redstone.setOutput(generatorSide, false)
    end
    sleep(1)
end