Never put the phone in rice.
Always take it immediately to someone that could remove the battery and then clean the phone/board circuits with a proper solution.
Because you let it dry in rice (which is the worst option) with still water inside, the circuits were slowly "burning" some components such as capacitors, maybe ICs, etc... Water keeps and makes new short circuits to electricity to flow. and sometimes things just burn. SO it was a bad thing to do and something got burn or the battery died by itself (due to the short circuit).
In my opinion, take it to someone that knows about these issues.... before it is too late!