Is my phone dead?

Hello, I am using galaxy S3 stock rom and my phone keeps shutting down/rebooting when I am using it. Sometimes I let it charge and 20 minutes later it turns off and I have to try many times to boot it. Many times I let my phone on airplane mode at night at 53% battery and It drains completely. I tried other batteries but still the same thing. Did anyone ever experience this?

Thanks

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