Rav 4 and battery problem, again?

It was started at 2 am last night.  I woke up in the middle of the night, knowing that it must be the jetlag that caused me to wake up for no good reason.  Suddenly, my obsessive compulsive instinct told myself that I should throw away all the garbage even though garbage pick up was still 2 days away.  That didn't stop me wrapping up all the garbage bags and moved them all to my Rav 4.  I was ready to drive to the nearby dumpster and throw away the garbage.

So I tried to start my car, and the moment I turned the car key, electricity went out.

I told myself: I've seen this before.  The battery connected was losen.

But then I thought, that didn't make sense, since my mechanic already replaced the old negative connector with a new one.  How could the connection being losen again within months?

Nevertheless, I opened the hook, and have a tiny wrench ready.  The negative connector looked dead tight.  But how about the positive connector?  Sure enough, the connection was a bit lose.  So I tighten the screw, and everything was working again.

Still, how come I keep running into this kind of problem?  Anyway, hopefully both battery connectors are tight enough so that the same problem won't happen again (until I change battery next time).