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Hello everyone!

Could GREATLY use help on this.

So as my above post mentions, I had the stock battery last for around 6 years / 60k miles. One day all of a sudden my bass amp (RF) just self destructed, and so did one of my JL Audio 10w3's. So bad, that the entire interior smelled like an electrical melt down! Pulled Sub box, and stopped using amp.

A month later, the stock battery would not start the car without a jump start. Took to dealership, had battery replaced. Everything was FINE.

Until about 2.5 weeks ago I stopped driving the car every day, and would let it sit in the garage for 2-3 days. Then one day it wouldn't start without a jump start. Then 2 days later, car starts on it's own just fine. Then a day after that, completely DEAD. Not a single light on the dash, nothing works at all. My tiny taclife jumpstart battery failed to work even after charging it to the max.

So called the insurance company, tow truck dude shows up with a giant jump start battery type (the blue one with the handle). Car turns over slowly and finally started after about 3-4 seconds.

Drive car straight to dealer - dealers tests battery and shows me a receipt tape like print out stating the battery they put in there 4 months ago is just fine.

Since then, I've been just disconnecting the negative terminal if I need to let the car sit for more than a few hours as I'm now working from home like everyone else.

One thing I've noticed, which is similar to others posts: the voltage meter.

Recently at stop lights, I notice the voltage drop to one tick below 14, and then if I'm driving for quite a while at 80+mph on the freeway, then it will slowly go back above to 14.1-3ish. In the past 6+ years of ownership, that battery voltage thing barely moved, and now it's moving around consistently, especially at stop lights. I've also had that strange idle rise/fall only once at a single stop light.

Other facts: 72,000 miles on the car now, serpentine belt has never been changed, stock alternator, battery replaced 4 months ago, and I did relocate to phoenix (hot as an oven) in January - The heat here kills just about everything, and I'm told by many that it's not uncommon to only get 18-24 months out of a typical battery. I did finally completely remove the dead RF amp that may have been doing some type of parasitic draw, but it does not seemed to have changed any behavior of the volt meter. Other than that, I'm running a 5 year old pioneer deck going to a 4 channel RF amp that was installed at a stereo shop. I did check to see if the amp that is working shuts off, and it does.

I'm open to suggestions on where to look next, and I may simply have to start with cheapest stuff first: serpentine belt ? (mine is about dead center per the diagram below)

Please advise if anyone has any ideas.