I bought a new battery a few months ago because the old battery was little swollen on both sides and I I have had a suspension fault message for some time. After a week I noticed the new battery was little swollen on the minus side but not on the plus side. I have kept using it beacause it has not got any worse. I have measured the new battery with multimeter and with the car on it shows about 13.8 but everywhere else I measured on the car it shows 14.25. With the car off there is now difference between the battery and the rest of the car.

 

Wherever you purchased your battery, you should take it back and have them check it. It should be under full warranty still and be replaced free if there's an issue.
A swollen battery is generally the result of a failing/failed cell that is expanding. Failure can occur for a number of reasons...poorly made, terminal corrosion, bad alternator over/under charging the system, etc...
Before replacing the existing one, be sure your battery terminals have no corrosion on them. If they do, replace either or both of them, you won't get the corrosion out.