2000 Toyota Camry speakers surged and lost all sound

What is your question?

I have a 2000 Toyota Camry le and here recently the back passenger side 6x9 speaker lost its sound, literally was just playing perfectly and then it just up and stopped. Tht other 5 speakers all still worked just fine. The front door speakers are getting pretty weak so we decided to swap out both the rear 6x9's and we were going to swap the door speakers out at the same time. So before we got into all that we were trying to figure out the reason as to why that 6x9 just up and quit like that, was it a short or bad soldering connection idk. So my buddy Informed me we could test the speaker itself to see if the speakers just a dud or if it still works using a drill battery. So he shoves the speaker wire into a 20v drill battery (???instead of a 9v battery???) And the connects the positive and negative to the 6x9 speaker. And as you can imagine it had a pretty decent zapping spark and now not a single speaker plays sound whatsoever. No fuses are blown? Is it the oem amplifier maybe..? Help