I had always used Gill G25s in my 172M, up until January of
this year. I always had slow cranking and sometimes no cranking
when the temp was 40 deg F or lower without charging the battery.

I made two changes in January.

I switched to the Concord RG-25XC and added the ability to connect
a DelTran Battery Tender when the airplane was in the hangar. During
the cooler months (can't say colder months since I'm in central Texas) I
use the Battery Tender between flight, but don't during the warmer months
(ok, ok during the hot months). If I recall correctly, the self discharge
of
the batterty is greater at high temperature rather than cold, so my useage
of the float charge might seem backward.

However, the charge voltage necessary to fully recharge the battery
increases
as temperature decreases. Therefore, unless the aircraft's voltage regulator
is
adjusted for temperature (which mine is not), at low temps the battery would
not be fully recharged during flight. If you adjust the voltage regulator
for proper
voltage to recharge the battyer during winter, it is too high for summer
operation.

Also, the ability of the battery to produce current is dimished as
temperature
drops. See the "Aircraft Battery Owner - Operator Manual" at this link
http://www.concordebattery.com/main_air_tech.php for Concord's view of
battery operation.

Therefore, I used the float charge during the winter months to get the
battery back
to 100% charged after each flight. Also, the fully charged state helped
provided the
heavier current required to turn over a cold soaked engine for the next
startup.

Anyway, since I made the change, I'm not once had the airplane fail to crank
and start, which I did numerous time before. Only time will tell how thie
Concord
RG-25XC holds up as compared to the Gill G-25, but so far it has been great.

Ronnie


"Doug Vetter" wrote in message
...
It's battery replacement time for the 172 and I'm contemplating the
installation of a sealed battery to eliminate the destructive corrosion
that's plaguing our new battery box.

I've done some research courtesy of google and the consensus appears to be
that the sealed units function equally well as wet cell units as long as
they're kept charged, preferably with a smart charger like a "Battery
Tender" that can properly float the battery.

Many of the threads I read were several years old so I'd like to solicit
some current opinions on the use of sealed batteries before I write the
check. Opinions?

-Doug

--
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Doug Vetter, ATP/CFI

http://www.dvatp.com
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