SadInfiniti

Something is wrong with my 2011 G37x coupe. It’s only got 125k miles on it, I’m expecting she’s good for quite a bit more. These last 2-3 years she’s sat/has not been run. I tried starting up the other day and the battery was dead, which I kind of expected having been left to sit for so long. I put a new battery in and tried starting and it didn’t work. The battery had drained a little from trying to start the car so I charged the battery, while connected in the car with a charger I have. I started it and it ran for a good 10 mins before dying, now the battery isdead again. Did I fry two batteries in a row by trying to start the car or is there another electrical issue at fault here? Does the electric starter or alternator charger cause issues like this? I think my battery is okay but I can always get a new one. I was planning on selling this car in the near future is this an expensive fix? Appreciate any help you can provide