2006 Acura TSX

-Car cranks slow every morning after sitting in both Winter and Summer. Consistently reads under 12v before starting (I check with a multi-meter)

-Car has killed one battery consistently every winter. (Likely from dropping so low every night for a year)

-Bought brand new AGM battery thinking it would fix the issue

-New AGM Battery still drops to under 12v from just one night of sitting. (started at 12.8v)

-Brought to 2 different autoshops who both did a standard parasitic drain test. Both reported back no drain or issue.

-Alternator has been tested and is charging and working fine.

However here is the thing. After both shops reported no parasitic drain. I told them that it was a brand new AGM battery to which they replied "Oh? That's weird. It shouldn't be that low from one night of sitting"

Both shops couldn't explain why my batteries voltage is getting so low from just one night of sitting but told me to keep an eye on it and kinda turned me away.

Anyone have any advice? These were just regular auto-shops that were quite busy, maybe I need to see a specialty auto electrical shop? Maybe the drain only happens when the car is locked and secured for awhile?

Any outside of the box suggestions?