Bill Daniels wrote:

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Mountain High says this about the Low Battery Warning:

The EDS model D-1 unit continuously monitors the condition of the battery
during operation. The unit flashes the red LED once every two seconds to
warn that the battery has dropped to about 6 volts. The unit will, however,
continue to operate properly for about four (4) hours @ 25° C after the
indicator starts to flash. It will flash the red LED once per second to warn
that the battery has dropped to about 5
volts and should then be replaced ASAP. The EDS model D1 will operate for 60
to 80 hours with a fresh alkaline battery under normal operation. However,
because a very small amount of current (»1 µa.) is drawn by the unit while
turned off, the battery life is about 4 to 6 months. Therefore, during long
term storage the battery should be removed. Once the battery drops below 5
volts the unit will stop
operating and the red LED will remain on.
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Of course this suggests the low-voltage warning will come on with 4 - 5
times as much life remaining in a lithium 9V but that's not necessarily a
bad thing. If the warning came on one hour after launching for a 1000k
attempt, I might feel comfortable continuing the flight with lithium but not
with alkaline.

My older model EDS has a battery test switch: steady light and sound,
battery OK; pulsing light and sound, only a few hours of life left. How
about the D1? If you test it as part of the pre-flight, you'll be able
to do that 1000K!


The above EDS alkaline battery life data is not especially comforting. A 4
hour margin after the low battery warning could cut short a long flight.
(If you even noticed the blinking red LED)

I check it when I check the oxygen level (most of the time).

If the alkaline battery is cold,
the margin could be even less. Lithium batteries are advertised to have
greater cold performance compared to alkaline.

At $6 for a lithium 9V vs. $2.50 for alkaline,

You are paying too much for your 9 V alkalines - they are half that at
places like Costco. Haven't seen the lithium units there, unfortunately.

lithium seems to be a really
good buy for any device that uses a standard 9V battery.

Until you forget to turn off the EDS, and a week or so later, it's dead.
A good thing for smoke detectors, for sure.

I use two alkaline batteries in my glider: one is in the EDS and serves
as the backup battery; the other (the primary battery) is velcroed to
the side of the unit and is plugged into the external power socket of
the EDS. If the primary, externally mounted battery dies, I just pull
the plug out of the EDS, and it switches to it's fresh internal battery.
It's an idea I got from Pat Martin.

--
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Eric Greenwell
Washington State
USA