To test converter functionality, measure, first, (from one battery terminal to the other) the voltage of the battery at rest with converter not powered. Second, measure voltage again with power to the converter.
The first measurement should be 12->12.7 DCV. The second measurement should be >13.2 DCV, likely > 13.6 DCV.
If your battery is now low and you have been connected to shore power for some rime, check the inline fuse or circuit breaker that is close to the battery. These are sometimes attached to the frame or tongue, occasionally inside a junction box. Without that circuit breaker closed, no power can reach the battery from the converter. Some breakers have a small reset button.
