Hi, just wanna give my contribution to the community.
Following is the serial gateway code with support of auto ID, which is still missing in the latest of MySensor (1.4) library (CMIIW).

links : bitbucket

@Fredrik-Carlsson info you havent got one, please check my development git

• Pulse sensor ( Watt, KWh and Ampere )
  {
  "id": "EnergySensor,
  "name": "Energy Sensor",
  "class": "MySensorsPulseMeter",
  "nodeid": 3,
  "batterySensor": true,
  "sensorid": 1,
  "appliedVoltage" : 220
  }