Battery life for a Uniden Dect 6.0 cordless phone

I have a Uniden Dect 6.0 cordless phone. It is several yeas old and has just started cutting out while speaking to anyone. How long should a battery for this phone last.?

Thanks for your interest, but my problem is solved. I discarded the Uniden Dect 6.0 and bought myself a Panasonic base and hand set, with rechargeable batteries. No further problems. Thank Heavens).