1991 xj6 battery dies

New battery last spring. Drive the car unti winter, the. It was garaged, with a battery tender. Started right up this spring. Drove the car periodically, no issues. Car sat for a couple of weeks, and wouldn’t start. Jumped the car, drove it around for at least 45 minutes. I tried starting the car 15 minutes after I drove it, and the battery was dead again. I’m not sure if it’s related, but as I parked it after my drive, I got a fuel fail 47 code as I put the car in park. Any ideas?

Faulty battery if alternator still charging, I had the same happen,2 months after buying a new battery, lucky I kept receipt, received a new one.they can die overnight.