I'm guessing your battery is a maintenance free acid lead battery. Using it for 25 months is pretty good.
To repair it, one has to have no materials and repair tools. It also takes a bit of skill. Maintenance of the battery is the 80s. At that time, electricity was unstable, people used it in black and white TV. Now people are rarely used. So there's no place to repair it if you want to.
So it's better to buy a new one. In addition, the battery can be used as long as it is 12 V. The bigger the VA, the bigger the volume, the longer it will last. The more VA you have, the longer it will last.
I don't know if your battery has a place to add vaporized water, you can open it to see if it is dry, add some vaporized water to charge and try, don't hold any hope. A well maintained battery like this will last about 2 years.