new 12 volt battey dying.

2012.
new 12 volt battery.
when the old battery died, i assumed it was old age and replaced it.
i am out of work with an injury, only using car once or twice a week, since i put in the new battery.
after sitting for 4 days, battery was dead. doors would not unlock. display would not light up when i opened the door.
assumed new battery was not fully charged, charged it for an hour. shop charger/starter, not a trickle charger.
next day, dead. jumped with portable jumper. drove for two hours, stopped twice. car started.
i am assuming it is not the battery because it holds the charge for a few hours.
i searched on here and saw similar problems with suggestions of a bad battery or onstar drain.
my onstar is not active.
i am thinking of charging and then disconnecting the battery and let it sit for 2 days.
if it starts, i believe that will eliminate the possibility that it is the battery.
if it starts, i will then try pulling the onstar fuse, F9, is it?

anyone have any thoughts or suggestions?