Sunway Solar Panel Charge Controller Regulator 20A 12V/24V with USB Port, Packed with 5pairs MC4 Connectors Female/Male for Solar Power Battery Charger System Kit

I connected the this to a 20w solar panel with a 12v 12ah SLA AGM battery and powering a 12v dc submersible pump. It ran for a day and a half then I noticed the pump shut off and the battery icon started blinking with the voltage indicator at 11.8v. Considering that I set the load off voltage to 11.6v I found it strange that the pump went off. At this time it was sunny so I was puzzled. I checked the voltage at the battery terminals and at the connectors of the charge controller. The the voltage at both points was 13.1v. I disconnected the pump and the battery from the charge controller in the night and connected the battery directly to the pump and it worked. I then reconnected the battery and the pump to the charge controller. It worked for about a minute then cut off again. I need this to work. It has only been a day and a half.