Is your trailer deep cycle 12 volt
battery dead? Are your trailer 12 volt
circuits not operating properly? Why are you checking the output of the univolt?.....
A univolt is not a sustitute for a 120 volt battery charger or a 12 volt
If your 12 volt battery for your trailer is dead it could have a bad cell or internal short circuit and not able to be charged....
Your car alternator/generator charges on a demand basis. Your 120 volt battery charger also charges on a demand basis. Both will not charge a bad battery. Depending on how many nights have been below freezing where you live, a partially discharged 12 volt battery may freeze....
I would start by taking your 12 volt deep cycle battery for your trailer to an auto parts store & have it tested. In the event your trailer does not currently have a 12 volt battery and never had a 12 volt battery, this would not apply.