I only use mine while it is plugged into our travel trailer with the trailer plugged into shore power. I verified that the trailer brings the battery to 13.50 volts. Measure someplace on the vehicle, I used the wire going to my cap light, with the vehicle off you should measure about 12.50 volts. With the ignition switch in ACC and the charger on you should get about 13.60. Probably your trickle charger just doesn’t provide enough current to overcome the load from the WiFi module.