It could be the aftermarket alarm is likely causing an issue. However, I don't think it would cause the alternator to fail to charge the battery. Is it possible for you to check it with a voltmeter or multimeter now? It's really easy to do. The link is listed above.
If you look at the attached pic, I need you to check a few fusible links. The pic is the entire wiring schematic for the charging system. If you follow the aforementioned link, that will tell me if power from the alternator is making it to the battery. If the battery is going dead when driving, either you have one heck of a draw or it isn't recharging. Pic 2 shows the orientation of the fusible link. Confirm there is power both in and out from the link.
Here is a link you may find helpful:
I'm not sure how Advance checked it, but usually, they are reliable. However, I need you to confirm it. Let me know what the voltages are both with the engine off and with it running.
Let me know what you find or if you have other questions.
Images (Click to enlarge)
Saturday, December 19th, 2020 AT 11:47 PM