Santa Fe (CM - 2007-12) :: Engine Dies While Driving And When Stopped

I bought my 2007 Santa Fe with 112,000 miles in April. It ran fine until about a month ago. When I turned the key to aux, the radio and lights came on but when I tried to start it I lost all power. Turning the key off and back on had no effect, it acted like the battery was dead. I opened the hood and noticed the pos cable was loose on the terminal. As soon as I touched it I heard a click, the security light started blinking and it started fine.

A week later as I was driving on the highway the electricity started blinking in and out and the car would shutter as it lost and regained power, then eventually died completely but the radio was still on. I got to the shoulder and tried to turn it back on but even though the radio and lights worked, nothing happened when I tried to start it. I lodged a matchstick between the pos terminal and the cable to make sure the connection was tight and it started. Driving home the power would occasionally stutter when I hit a bump but it never died completely.

I used a battery and alternator tester that plugs into the cigarette lighter and both registered as fine. I've driven it to work, about 2 miles, several times since and the power sometimes cuts out at bumpy parts of the road and it has died completely twice while sitting still at a light. The clock doesn't reset when it dies so, knowing nothing about electrical systems, I would guess that the electricity isn't being entirely lost. Every time it dies the radio and lights still come on but I have to get out and jiggle the pos cable to get it to restart. While driving the battery and seat belt lights flash randomly. A friend told me to try removing the pos cable while it's running and that if it died, it was probably the alternator. Tried it and the engine died immediately. Don't know what this means since the alternator tested fine.