On Wed, 03 Dec 2014 20:08:56 -0800, Dave Leonard wrote:

The Garmin GPS-25 manual indicates the internal battery is a
rechargeable Lithium with a capacity of about 180 mAh. It also says the
load on the battery when the board is unpowered is 50 microamps. There
is no way to see what the state of charge is on that little battery. Or
how long it takes to charge it up when the board is powered. A fully
charged battery is good for about 5 months. If you discharge the battery
completely, the memory and real time clock will quit and you are back to
19.5 years ago again with no way to fix it other than sending it back
again. So don't go too far between the new battery install and using the
gps again.


Right, the manual says "up to six month charge" for that battery.
Extremely marginal for the way we commonly use the units. Since the
firmware worked correctly without battery backup for roughly the period
2005 +- 10 years, it covered up bad batteries, or good batteries that
just had been discharged. Without new firmwware to kick the can down the
road again, it's going to be on an ongoing headache.

Newer systems use a 13 bit integer instead of 10 to keep track of the
week, doubt there's any chance that would ever be retrofit into the units.

-Dave