A digital volt meter is not really expensive. You can get cheap ones at a hardware store. Check the voltage of the battery it should be about 12 V. If there is a current draw running the battery down, it's just detective work to find it. Try pulling fuses until you find the circuit with the problem and then troubleshoot that.
BTW, DON'T draw an arc off the battery terminals. That's how batteries blow up.
Have you made sure the battery terminals are clean and have a good, tight connection to the battery?
Check the wires that run from the alternator to the battery. There may be damage to the wire causing poor charging of the battery sometimes. Make sure all wires on the alternator are connected securely and that there is no corrosion or dirt build up there too.
Even though the test at Autozone showed a good battery, you might consider the possibility that the test was wrong and try replacing the battery anyway. You can do a test on your alternator yourself. If you can unhook the battery while the car is running and the car stays on, then the alternator is good. If the car dies when you unhook the positive battery cable, then the alternator is bad.
Buy a multimeter or DVOM that is amp readings capable ...cheaper basic models sold at home centers, etc.. for around 10-15.00 ...and check battery voltage and alternator output....a fully charged battery should read around 12.6-12.7 volts and when the car is running, the alternator charge rate should read around 13.5 -14.5 volts at normal temps and a good battery.
http://www.aa1car.com/library/charging_c...
You should also test for an excessive draw or drain on the electrical system/battery....anything exceeding 40-50 milliamps is possibly due to bad wiring/poor connections, bad windings/internal short in a fan or wiper motor, short in wiring, lights staying on, a bad power port or lighter port grounding out, etc.. Check the wiring for any add-on items like subs/amps, lighting, etc..and make sure it's not shorting to ground or other issues.
Use the multimeter or DVOM to check the circuits by installing the meter probes between the battery negative cable and negative terminal and pulling fuses one at a time until the draw on the battery drops...see video below.
Alternator.
My car battery in my 01 Grand Cherokee is been a real B**** lately. I have subs and amp. I also have led lights on this inside. But all have been unplugged for an extended amount of time and it still dies without them being plugged up for about a month now. Now, it will either be extremely slow to crank in the AM like the fly wheel is really slowly turning, or it will be dead. Then i go to school for about 7-8 hours and it will be the same. Dead or really slow to crank. And it shows signs that my battery has leaked acid. But my battery checked out ok at autozone. And my alternator did too. And today when we jumped it off the positive terminal sparked. Not a little pop like a big spark and that was when I tried to crank it. All lights inside stay off the radio is led lights arent even hooked up neither is my amp. What the hell is drawing power? Or what did it spark like that for? Cant afford to take to a shop or anything right now so this is my last hope.
