On Sat, 07 Jul 2007 12:03:28 -0700, Ron Wanttaja
wrote:

Lately, though, my voltmeter has been running a bit low, both before the engine
starts and when the plane is cruising. My Microair transponder has a voltmeter
function, and I've verified that the battery is running about a half-volt lower
than I'm used to.

For a healthy battery with no load, a half-volt drop at the terminals
would represent a battery that is at an approximate 60% state of
charge.

The engine starts so quickly I can't really tell if the battery charge is low.

For a sealed battery, the only way to really know battery health is to
take it out of the airplane and test its capacity with a known load.
Since most of us don't have the wherewithal do to that sort of thing,
the purchase of a new battery is our only reasonable option.

Anyway, I was figuring I had more problems with the generator/regulator, but
when I put an external charger on the plane this morning, the initial charge
current was quite a bit lower than I'm used to seeing when a battery is low on
charge.

The lower voltage at no load is unusual. Have you measured the
voltage at the battery terminals? That would eliminate a systematic
issue in your electrical system. And a lower-than-expected charge
current could indicate that the battery really has a good charge.

Assuming that it really is a bad battery--and this is just a guess--
there could be a separation of one plate from its absorbed glass mat.
This would leave it functional, but it would operate like a battery
with less capacity. Alternately, if the battery was ever kept in a
discharged state too long, it could be sulfation.

http://en.wikipedia.org/wiki/Sulfation

Perhaps a call to Odyssey is in order. They might have an interest in
an early failure, or at least know the failure modes of their product.
They have a toll-free number (800-538-3627).

So my questions run down to:

1. What kind of life are people getting with these Odyssey batteries

I got six years on an older Genesis battery and my present Odyssey (a
PC925) is still going strong after four years.

2. When they fail, what kind of indicators do you see? Does it just suddenly
refuse to hold a charge, or are there early warning signs?

The Genesis just wouldn't hold a charge. The symptom was an engine
that had difficulty cranking in cold weather.

Rob-
__________________________________________________ _
Rob Cherney rcherney(at)comcast(dot)net
Ellicott City, Maryland