Unless the battery has run dry or been abused in some other way, such as flattening it and not re-charging it for a period, or your conditioner being faulty, I would say the batt is faulty. At under a year it must be under warranty?
IF the conditioner were duff and putting out too high a voltage that would damage the batt but would also cause the cells to dry up. If you check the voltage the condtioner is putting out (maybe when connected to a known good battery) and it's ok then it sounds like the banner.
I would expect 3 yrs upwards from a batt that has been looked after.
Graham