Davie, the best you can do for a battery when not in use is to take it home, and keep it fully charged.
There has been a lot of talk about where to keep batteries, but the general consensus is to keep it somewhere cool, but frost free, and not stored directly on a concrete floor.
Placing it on some thick cardboard or wooden board seem to be the preferred methods.
It is preferable, but not absolutely essential that you use a multi stage charger which will charge the battery, then go to "maintainenece" mode to keep it fully charged.
Once a battery loses charge, sulphation of the internal plates starts to take place, rendering the battery useless.
Try taking yours home and giving it a full charge and see how it responds, if it will not hold charge, a new battery is going to be needed.