Etios head unit flickering & resetting when ignition is off

Suspected the ignition switch at first, but then looking under the bonnet, I found the battery had huge chunks of plastic eaten away by rats.

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Recently started noticing the head unit in my Etios resets itself when parked overnight.The lights and screen flicker sometimes even when the key is not in the ignition as seen below. The radio also has a loud whining noise in a few audio settings.

Suspected the ignition switch at first, but then looking under the bonnet, I found the battery had huge chunks of plastic eaten away by rats. Not sure if this problem started before or after the rats invaded the poor car.

So far I've looked through the engine bay and under all dashboard and kick panels looking for rat bites but I really can't find anything.

The only thing that raised suspicion was this rusty looking ground point which the head unit is directly grounded to.

This point is inaccessible as I'll have to take down the entire dashboard to clean this. Will I just be able to wire a new ground to any other ground point in the car? Not sure if this would fix it but any help or inputs would be greatly appreciated!

Update: Wired a new ground and radio whining noise and flickering hasn't stopped.

I checked the radio ACC wire with a multimeter while the car was off and key out and there was slight voltage (about 0.4 to 1.2v). Sometimes it goes back to 0v after a while. The multimeter shows full 12v when the key is turned to ACC.

ACC when key out:

ACC when key turned:

I'm suspecting a faulty ignition switch or possibly a bite in the wire that's shorting the Constant and ACC wire. How does one test an ignition switch? Any help to isolate this issue would be great.

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