Depending on the firmware on your battery, it may not have the latest self-discharge routine. The newer firmware has the battery discharge to about 50% after 48 hours (IIRC). The idea is to prevent users from storing FULL batteries - something that will drastically shorten the battery life.
I didn't know that storing them full was bad, and about 8 months in, one swelled, and did exactly what you described. I contacted DJI, who said the battery warranty is 90 days (or maybe 6 months, I don't remember) - but I was on my own.
FWIW, you can buy
this third-party battery from Banggood. It's less than half the cost, and has an awesome OLED display that provides all sorts of practical info (time remaining till empty, total flight time, voltage per cell, how many charge cycles, percent of battery health, and while charging, temperature, time remaining till full, current and voltage, etc). I got a solid 20 min flight time on the very first flight with it.
I don't know if this battery has the self-discharge firmware, but with the display it's easy to verify the status.