Had the 'replace battery' alarm some time back so I dutifully charged out and got ripped off IMHO for a replacement 12V SLA battery which fixed the alarm problem (wasn't really a big deal). Did some tests on the old battery and it was absolutely fine with no degradation I could measure so I kept it charged up in tiptop condition until I got the 'replace battery' alarm again exactly 12 months after the last time it was replaced. Not coincidentally the first time I got that alarm it was exactly a year or 2 pretty much to the day from when the NBN was installed. So I shut down the NTD power supply and swapped back to the original battery (fully charged), fired the power supply up and all is good again.

So I have to conclude that the 'replace battery' alarm is not based on battery condition but initiated arbitrarily by the ISP based on a simple timer. Seemed more than coincidental that the battery vendor had a rather large stack of these replacement batteries for a steady stream of eager customers at $45/battery, most of whom wouldn't check to see if the battery actually needed replacing as I did. Must be a lot of these batteries being thrown out unnecessarily not to mention the probability of some sharks making a living out of supplying and replacing batteries.

Anyone here know more about this?