I recently purchased converter P/N 091029US from Amazon to use as a 13.15V trickle charger. I assembled and bench tested the unit and it appeared to work as expected without a load. I could adjust the output from 22V to 12V using 24V input. My fully charged wet lead acid battery (charged for 24 hours and rested for 4 hours) measured 13.15V. I adjusted the Drok output to 13.15V and attached it to my battery. The output V display immediately dropped to 0.1V. It seemed to have failed. I unplugged it and tried it again several times but it has no output. What happened? What do I do now?

Thank you for helping