Its sealed unlike a car battery so there is no fix for it. Replace it is one option, but if you dont like your neighbours you could not bother with a battery at all, then in every powercut the external sounder will sound and upset them. Or if you like to gamble you could just leave the battery in the panel may catch fire, it may not. To be fair never heard of one catching fire in a house (an engineers van caught fire recently due to old batteries) but there is always a first time. If you dont like the sound of those options you should either, replace the battery, get the alarm serviced, or decommission the system completely