Dead car battery turns on after jumpstarting but dies again as soon as I try starting the car (car sat for 4 months)

My car's been sitting for 6 months, however at 2 months my family started it and it started. Now 4 momths since then, I tried jumpstarting my car from another car and it turned on instantly and started blaring the alarm. We let it charge for about 5 mins before starting the engine but it died as soon as I tried to start the engine. The car would turn back on though immediately since it was still connected to the other car. We tried pressing the gas on the other car which then popped open the trunk automatically but the car still didn't start. We thought it was the dead car key (got a message on my dash) so we replaced the battery in there but that still didn't do it. Overall the cables were connected for 20-25 mins. What can I do?