I will assume that your battery is a LiPo (Lithium=Polymer), Where did you have it stored when not in use? I'm betting it is
a LiPo. Unlike NiCd batteries, LiPo batteries are environmentally friendly. But for safety reasons. it is best that LiPo cells be fully
discharged before disposal. In your case, temperature variations, any cell in the pack has been physically damaged will result in
a swollen cell or a split or tear in the cell's foil coverage, Since yours is swollen, DO NOT discharge the batt. Prepare a plastic
bucket with a gallon of water mixed with about a half a cup of salt. Drop the battery in the salt water and let it sit for approx.
2 weeks. After that you can wrap it up in newspaper for the landfill. Look on line for radio controlled planes, autos, drones etc..
(HobbyKing) for LiPo's. Hope this info helped you out. Let me know how it went,