I have a couple of questions:
Why the side of a battery is bulging?
Is a battery with a bulging side ruined?
The bulging is caused by gassing. This is caused by overcharging or by a short circuit inside the battery. The acid inside the battery is turned to gas and it expands the sides of the battery.
to the question ... is it ruined? .... i would consider buying a new one ASAP ... shop around, there are places that "rebuild" batteries and sell them much cheaper than retail ($25 and up)....get in the yellow pages and start calling around...