Startup issue- possible ground wire/battery terminal?

[HANDUH]

I have a problem with my 2005 civic ex coupe. So first of all this might be a little long but let me explain the issue. I bought the car a month ago, I have only driven it 4 times total and have already had 2 occurrences where it wouldn't start. The guy I bought it from said he has had issues with ground wires in the past but said it has been a few years n he thought it was fixed. So I took it to a shop the first time it wouldn't start n he said some of the ground wires and terminal were loose so he tightened them down and also tightened the battery down, two days later I start the car let it warm up go back out to it and it's running but my radio is off and all gauges are at 0 or dead like the car isn't started( but it was running) I didn't know what to do so I tried to see if the terminals were loose or the ground wire connections and from what I found they were still tight . Went to try again and it started somehow even though I didn't tighten anything. I tried again today and it started just fine again...so idk what the issue is because I didn't really do anything between it not starting and starting again, anyone with suggestions

 

[HeX]

Have you inspected the wiring in this car to see if its been hacked into before? Does it have any kind of swap?

 

[HANDUH]

I had a mechanic look at the wiring and battery /battery terminals and do some testing for amperage all he said he could find was that the terminal and wires were loose so he tightened them up and tightened the battery down more, been 2 days since then n it didn't start again on me last night. I know it does have aftermarket ground wires that are bigger due to aftermarket HIDs (per the seller)

 

[Wannabe Mechanic]

I'm having a similar problem with my 1996 Civic LX. It has a new alternator, batter, and the starter works, but the car is dead every 2-3 days after not using the car.

The car is pretty stock. I put in a new radio and the connections are tight. It also did this once or twice before the radio was installed. I can't figure out what is grounding out the battery. Are there any common grounding issues with the 6th generation Civics?