My system is gear drive slide. It requires many amps so they run an individual 6 gauge wire just for the slide and the relays. Even if yours is hydraulic it will still draw many amps.
Find out why the batteries are dead. You know the converter is working because the lights work but you need to use a voltmeter on the batteries and find out what happened. Did it blow a fuse? Etc.
Was something left disconnected after repairing the hyd hose? Start at the battery and back track. You should see about 12 volts on the battery and about 13.6 to 14 plus when it's charging.