This is the answer I got from VR concerning the "E" display. Hi,
The E display indicates that our technicians need to look at the unit. The cause could be a part malfunction. It could be caused by the electrical system of the vehicle in which it was used. It could be caused by using wiring that is not Valentine One wiring or a homemade cord not used with a Valentine One lighter adapter or Valentine On direct-wiring kit. Thank you for emailing us.