I think what happened was that because it is winter time, the sensor is unable to maintain the battery level as the sunlight is weaker than summer time.
Do you have an incandescent lamp at home? If so, can you try to charge the sensor under the incandescent lamp (distance between the solar panel and the lamp should be around 10cm) for a couple of days.
Please let us know if it works.
Could you please send us email to email@example.com with your Netro account registered email?
We will have our technician look to this issue.