Exide Battery
Attery replacement not given after found the one sell is weak charging

I bought exide home used battery on 12.03.2012.

from last month we are getting proper back up.

now the service provider saying that one of the cell charging is weak condition. when i asked to provide the replacement they said wont give for this and all. ask them to use the same battery if again we found the problem come back nu.

pls suggest how to get the replacement for this.