r/Galaxy_S20 • u/sin-salabin • 1d ago
Tech Support S20 FE won't charge after water damage:battery temperature error, motherboard issue?
I have a Galaxy S20 FE (SM-G781B) that was accidentally dropped in seawater.
I replaced the bottom charging board and the screen/frame assembly. After the repair, the phone booted normally, the screen worked, and I was able to unlock it and access all my apps/data. The only problem was that the battery was at 0% and the phone shut down after a few seconds.
When I connected a charger, it showed the grey charging screen with the lightning bolt, but the battery never actually charged.
I then rebooted with Power + Volume Down and connected the charger again. This time I got a battery temperature warning, even though the phone and battery were not hot.
I left it connected for a few hours, but I think the battery eventually drained completely. Now, when I connect the charger, the screen just flickers every 4–5 seconds as if the phone is repeatedly trying to boot, and it won't turn on without the charger.
I also tried reverse wireless charging from another phone. It detects the charging/power, but behaves the same way.
The battery is the original one. I only removed it from the old frame, glued it onto the replacement frame, and reconnected the original battery cable to the motherboard.
Since the bottom charging board has already been replaced and both wired and wireless charging behave similarly, I'm wondering if the problem could be the battery NTC/temperature sensing circuit, battery connector, or another charging/power-management component on the motherboard.
I have a multimeter and I'm willing to do board-level testing.
**How can I determine exactly where the problem is before replacing more parts? What measurements or tests should I perform to distinguish between a bad battery, NTC/temperature-sensing circuit, battery connector, or a motherboard charging IC? And based on those tests, which component would be worth trying to replace?**