[1000mp] 1000 mp Battery

[NOEL POULIN]

Hello
I have a question about the backup battery. I bought the radio last Feb(2005)...I replaced the back up battery in last August....and now I notice that I will have to replace it again....cause, the settings are not there anymore....
I wonder if anybody had the same experience with this battery.
What could be the cause????I have two mark V and they have the same problem....have to change battery every 5 or 6 months...It is not normal according to the instruction  manual.....they say it i s supposed to be good for at least 5 years....anybody help??????
Thanks
NOEL