How to charge battery using engine power

I'm new to BeamNG lua programing.
I am trying to program a powertrain Lua based on

Code:

/lua/vehicle/powertrain/combustionEngine.lua

I create a variable "device.chargeEnergy" which equals to "device.spentEnergy" to calculate how much energy will be charged to the battery. Then I edited local function "updateFuelUsage" to update energy consumption.

Code:

local function updateBatteryStorageRatios(device)
  for _, s in pairs(device.registeredBatteryStorages) do
    local storage = energyStorage.getStorage(s)
    if storage and storage.energyType == "electricEnergy" then
      if storage.storedEnergy > 0 then
        device.batteryStorageRatios[storage.name] = 1 / device.storageWithBatteryCounter
      else
        device.batteryStorageRatios[storage.name] = 0
      end
    end
  end
end

local function updateFuelUsage(device)
  if not device.energyStorage then
    return
  end

  local hasFuel = false
  local previousTankCount = device.storageWithEnergyCounter
  local previousBatteryCount = device.storageWithBatteryCounter
  local remainingFuelRatio = 0
  local remainingBatteryRatio = 0
  for _, s in pairs(device.registeredEnergyStorages) do
    local storage = energyStorage.getStorage(s)
    if storage and storage.energyType == device.requiredEnergyType then
      --guihooks.message({txt = "Debug1", context = {ttl = 3, color = "info"}})
      --guihooks.message({txt = "Required energy type:" .. string.format("%s", device.requiredEnergyType), context = {ttl = 3, color = "info"}})
      local previous = device.previousEnergyLevels[storage.name]
      storage.storedEnergy = max(storage.storedEnergy - (device.spentEnergy * device.energyStorageRatios[storage.name]), 0)
      if previous > 0 and storage.storedEnergy <= 0 then
        device.storageWithEnergyCounter = device.storageWithEnergyCounter - 1
      elseif previous <= 0 and storage.storedEnergy > 0 then
        device.storageWithEnergyCounter = device.storageWithEnergyCounter + 1
      end
      device.previousEnergyLevels[storage.name] = storage.storedEnergy
      hasFuel = hasFuel or storage.storedEnergy > 0
      remainingFuelRatio = remainingFuelRatio + storage.remainingRatio
    end
  end
 
  for _, s in pairs(device.registeredBatteryStorages) do
    guihooks.message({txt = "Debug", context = {ttl = 3, color = "info"}})
    local storage = energyStorage.getStorage(s)
    if storage and storage.energyType == electricEnergy then
      local previous = device.previousEnergyLevels[storage.name]
      storage.storedEnergy = max(storage.storedEnergy + (device.chargeEnergy * device.batteryStorageRatios[storage.name]), 0)
      guihooks.message({txt = "Stored Energy" .. string.format("%.2f", storage.storedEnergy), context = {ttl = 3, color = "info"}})
      if previous > 0 and storage.storedEnergy <= 0 then
        device.storageWithBatteryCounter = device.storageWithBatteryCounter - 1
      elseif previous <= 0 and storage.storedEnergy > 0 then
        device.storageWithBatteryCounter = device.storageWithBatteryCounter + 1
      end
      device.previousBatteryLevels[storage.name] = storage.storedEnergy
      remainingBatteryRatio = remainingBatteryRatio + storage.remainingRatio
    end
  end

  if previousTankCount ~= device.storageWithEnergyCounter then
    device:updateEnergyStorageRatios()
  end

  if previousBatteryCount ~= device.storageWithBatteryCounter then
    device:updateBatteryStorageRatios()
  end

  device.chargeEnergy = 0

  if not hasFuel and device.hasFuel then
    device:disable()
  elseif hasFuel and not device.hasFuel then
    device:enable()
  end

  device.hasFuel = hasFuel
  device.remainingFuelRatio = remainingFuelRatio / device.storageWithEnergyCounter
  device.remainingBatteryRatio = remainingBatteryRatio / device.storageWithBatteryCounter
end

However, the battery cannot be charged. I am wondering how I can charge energy produced by engine into the battery.