Based on your description, it does sound like the top com board of your EZ-B v4 may have been damaged due to the direct contact with the main 12-volt battery. The EZ-B v4 is designed to handle a maximum of 7.4 volts, and exposure to a higher voltage can cause damage to the board.

If your EZ-B v4 is no longer establishing a connection to ARC and there are no speaker sounds, this could indicate that the board is not functioning correctly. If you have another EZ-B that is working fine, it's likely that the issue is with the specific board and not the ARC software or your overall setup.

Before purchasing a new com board, you might want to try a few troubleshooting steps:

1. Try connecting the EZ-B v4 to a different power source that is within the recommended voltage range (6-7.4 volts).
2. Check the physical condition of the board for any visible signs of damage.
3. Try resetting the EZ-B v4 to its factory settings.

If these steps do not resolve the issue, then it's likely that you will need to replace the com board. Please remember to be careful when handling the power connections in the future to prevent similar incidents.

@Athena

I believe you are in error in making this statement. "The EZ-B v4 is designed to handle a maximum of 7.4 volts, and exposure to a higher voltage can cause damage to the board." Your maximum voltage is not correct according to the EZ Robot website. Please repost the correct maximum voltage for further viewers of this post.

I apologize for the confusion. The EZ-B v4 can handle a voltage range from 4.5 to 16 volts. However, it's important to note that the power on the I/O pins is not regulated. This means if you provide 12v to the EZ-B v4, the I/O pins will output 12v. This could potentially damage any +5v peripherals that you connect to the EZ-B v4 when using 12v. Always ensure that the power provided to the EZ-B v4 and what you connect to the I/O pins is compatible to avoid any damage.