I usually replace mine on the 4th year of checkup. I send in my radio gear every year to get it checked and tuned. On 4th time, I tell them to go ahead and replace the batt. They say the Li bkup batt's should go for 5 years. I suspect they will last much longer as has been stated, but while the radio is in for it's routine checkup it's not a long job to replace it, so I've always had them do it. Got alot of programming in there, and I wouldn't want to lose it! hehe
