Hi and welcome to the forum
That is odd
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I’ve never seen a blinking red light by the camera, do you mean to the left of the ear speaker, the camera is to the left of the ear speaker
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The phone will not work without the battery. The power goes via the bottom module USB C port to the power chips on the core module. The core module communicates with the battery to see what charge is viable.
You may still have damp issues and maybe some contacts are tarnished and hence there is no signal to charge or power on.
The battery maybe completely discharged and if so you will have to leave it plugged in for some hours for it to gradually accept any charge.
So
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Check the b battery voltage. If it’s 3.8V that around 40% charge and should power onand if not then it’s not a charging or battery issue
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If the voltage is 3,5V or lower then you will have to try and charge it slowly or alternatively externally to the phone.
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Check the battery isn’t distorted ~ battery spin test
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See this post for links and ideas
Removing the bottom module requires removing the display module where you have access to it’s contacts and can check for
[red square]
[red solder] etc.
The two links above are just odd posts from FP3 charging topics