Modicon Quantum TX Battery Back-Up

[pitbull2]

I have a 9 month old modicon quantum tx plc with a 434 cpu. Since it's installation I have experienced problems with the battery back-up not working after a power failure (planned or otherwise) to the plc. Despite changing the battery, and the fault light not being on the plc always boots up from the eeprom after a power failure. While this in itself is not a major problem I am still losing any data in the plc which has been altered since the last time the eeprom was blown. Has anyone suffered similar problems and if so can they suggest a possible cure?
Thanks.