I have a s6 edge 925t recovered from water damage with similar problems, It seems to discharge quickly even when powered off. Replaced bat. I noticed a lot of corrosion around the battery connector on the motherboard, and cleaned as best I could with ipa, ultrasonic cleaner, and tried reflowing the connectors in the area.
You really need to get out the microscope or magnifying lens with light and look over the whole board closely to see any possible bridged connections or loose connections. Also check the pins on the flex cables and connectors.
Mine worked fine for awhile but now back to discharging the battery when powered off. any input appreciated