"Robert Neville" wrote in message
...
"Joe J" wrote:

No manual, just wondering how long they last when they are AC wired? I
know
battery only, they recommend once or twice a year, but what about AC
powered? I would think several years, no?

If you are using standard alkaline, once a year unless you like getting
woken up
at 3AM on a random day. Once every 10 years if you buy 9v lithium.

That means I probably shouldn't be checking on the lithium battery's voltage
every year. (-: I just started using them and I've been measuring the
voltage drop (very, very little) each year to try to estimate how long
they'll last. If I get ten years out of one, then it's actually cheaper to
use than alkalines in the long run, and a hell of a lot more convenient,
providing I can get over my paranoia about them failing suddenly. (-:

--
Bobby G.