AGM Battery Dead or Phantom Draw?

Thank you in advance for everyone's help in solving my issue/providing guidance!

I bought a Diehard Platinum AGM battery January 2021 and never had any issues. ScanGauge II said voltage was 14.0V with the truck running and never had to jump start the truck as I was driving it at least every other day.

I started working from home in November 2021 so only drove the truck 1-2 times a week, at this same time I installed a RoughCountry Speedometer Calibrator device. This is when I started having problems.

Since November I've had to jump start the truck if its been sitting for more than a day or two. Battery was reading 10V before jump starting so I jump started the truck and took it to Advance Auto. Battery of course tested fine and Scan-Gage II was reading 13.4-14V while the truck was running.

(2) days later truck wouldn't start and read 10V again, so this time I took the battery in hand to Advance Auto to have them test it. They said battery tested fine but needed to be charged. Left it with them to trickle charge overnight.

Picked up the battery the next day (1/17/22) which was fully charged to 12V when I double checked it with a multi-meter.

Still haven't been driving the truck much only 1-2 times a week due to fuel costs and no place to go. Fast forward to today I unlock the truck to find no interior lights turn on. Woke up the Scan-Gage to find voltage reading was 7V with the truck OFF and mid 40 degrees here in S. Carolina.

I'm afraid to take the battery back to Advance Auto for them to tell me it only needs to be charged again. Yes, I've ordered the HKB fuse but still hasn't shipped out.

Is this a phantom draw issue or could I have already killed the capacity of the AGM battery? I'm not sure how to check for a phantom draw but the last modification I made was the speedometer calibrator module.

Thank you again for any advice as to where to start!

 

There are some thread going on now, but my understanding is that the stock configuration does not charge at sufficient volts in order to fully charge an AGM battery.

https://www.tundras.com/threads/battery-monitor.101819/page-2