3 is the long post that goes to the bottom of the battery tray to the top of the battery. It screws down to #2 which crosses over the battery. It just holds the battery down into the car.
I see no wing nuts/bolts on any pictures of 9th gen r18 engine pics. Maybe the person who had your car...
it's just a standard nut from factory
https://www.collegehillshondaparts.com/v-2014-honda-civic-sedan--ex--variable/electrical-exhaust-heater-fuel--battery-1-8l
Look at my 2nd pic above. It can be set to unlock all doors on the remote.
“Door lock mode”. One press unlock / (driver door/all doors). Yours is clearly set to all doors.
I think you’ll find all over the forum that users advise going aftermarket for more/better functionality. some info about 14/15 ex radios in the lx.
http://9thcivic.com/forum/threads/2014-15-ex-radio-in-your-lx.15650/
what's your dash/radio look like? Pic? I don't know if you get the same model the US/Canada gets or not. There are even some differences between the US/Canada radio/hvac. You'll likely not be able to get a correct answer unless you find someone else with your exact setup in your region...
There is a harness for the steering wheel controls for aftermarket radios. So, they would have installed that. If you didn’t remove that, you still have that all hooked up to the oem radio. Same with your bypass switch/Bluetooth. Why did you remove the radio