2005 Pontiac Grand Am battery problem

I seem to have a battery,or battery terminal or starter problem? For 3 days my car would have to be jumped, but when i turned it off it would have no power whatsever. I tightened the battery terminals then I had no problems for about 1 week and couple days then it has no power again whatsever. I unconnected the terminals then connected. Nothing happend. I had the battery tested it when I jumped it it tested good same with alternator. Any one know what i can do to fix this

Replace both the battery and negative cables on the car. In the absence of any tools to diagnose what’s going on, that’s where I’d throw money and time. That is assuming you don’t have access to a volt-ohm meter.

Now, if you are willing to buy (or borrow) a volt-ohm meter, sometimes called a DVM, to test the cables, maybe we can help you find the problem, save some money and reduce frustration. So can you get a DVM?

I figured out the problem. My sub was draining the battery. So I just unplugged it. Battery and terminals are good. Thanks