Swollen hardcase lipo - dangerous?

[Cardnim]

Hi guys,

Im new to lipo batts, but have used two for the last month with no worries.
Yesterday, I had a bit of binding happening in my Cat SX so set about to find where it was occuring.

To test it, I then plugged in the lipo (I didnt use the battery strap but just had it sitting in situ on the chassis) and then set my throttle hold on the TX to 50% power and ran it for 5 minutes.

Good news: the motor didnt get warm and the binding is resolved.

Bad news: the hardcase lipo swelled slightly.

I immediately shut down the system, unplugged it and took it outside where it spent the night under shelter, but outdoors. This morning, it is no different: the swelling is still there.

Is this normal (Im guessing not). Why did this happen? and I guess my battery is now dangerous and useless?

The setup:
Speed Passion GT2 LPF esc
Speed Passion 6.5T motor
GM Racing 5400mAH 7.4v lipo (2 cell, 45C rating)

Any advice?

Thanks guys - Im a bit worried that this thing is about to go pop and Ive just blown up £45.