I'm not finding the 21 day spec for the '25 in a quick search, but here
it is on page 3 for the '15:

https://static.garmincdn.com/pumac/G...ifications.pdf

There are multiple variants for both the '25 and '15, perhaps that is
confusing the issue.

Certainly the selection of suitable engines was limited back in those
days, but the FR vendors could have done a better job of documenting the
issue, or even providing additional batteries in their units to mitigate
the problem. My ancient backpacker gps still has the correct date
today, probably because it has AA batteries installed at all times
except when changing them.

Dave




On 2/24/19 11:05 AM, Tim Newport-Peace wrote:
Interesting. I have a Garmin Specification that says the backup power is
"up to 6 months". However, whatever it is, it will reduce with ago.

As for the choice of components, it was what was available at the time,
which was a long time ago.

At 17:36 24 February 2019, kinsell wrote:
3. also depends on what firmware is loaded


The popular GPS25 engine, used in the really old FR's, had a firmware
update released in 2000, just after the start of the second epoch.

The GPS15, a newer, drop-in replacement for the 25, had numerous
firmware updates released through 2009 I believe. It's possible to rig
the firmware to provide 1024 weeks of trouble-free operation from any
given arbitrary date. Maybe they did that, maybe not. It's called
"setting a pivot point" by the manufacturers.

Both the '25 and the '15 have data sheets when say the internal
batteries provide "up to 21 days" of keeping the RTC data alive. You
can't really blame Garmin for the problems in the flight recorders, it
was a poor choice of components on the part of Cambridge and others to
use these things in FR's that likely sit six months without charging in
the off season.

-Dave





On 2/24/19 8:33 AM, Tim Newport-Peace wrote:
Known issue, see http://tinyurl.com/y56n8odz

If it will effect your Flight Recorder depends on:

1. The ago of the GPS Engine in your recorder.
2. The condition of the RTC battery in the GPS Engine.

After 6th April 2019, you can check the date by downloading a flight
made
after 6th April 2019 and opening the .IGC file with a text editor, such
as
Wordpad. Within the first few records you will find a line beginning
“HFDTE” followed by a date, if this is the date of the
flight, then you
are fine, otherwise you have a problem. Talk to your dealer.