Battery heater: Any experiences?

Newps wrote:
nrp wrote:
Maybe you can get to the clock terminal with a trickle charger lead?
You only need & want maybe 100 milli-amps if even that much.

You can get a 1 amp trickle charger at the auto parts store. You will
never hurt the battery at a constant 1 amp.

You probably won't hurt the battery itself (plates, case), but if it's a
flooded battery, the electrolyte will tend to go away.

The average cheap "trickle charger" is not regulated in any way, and
depends on the user shutting off the charger after a certain time.
These are commonly sold as a motorcycle battery charger, with output of
1 A at 12 V (and sometimes 6 V). These are great for charging smaller
batteries when you don't want to use a "big" charger (6 A, 10 A, or 12 A),
and for playing certain tricks on an elderly big battery when you are
trying to squeeze a little more life out of it (ground vehicles only).
But if you hook one up to a flooded battery and leave it long enough,
you'll start overcharging the battery and cooking off some of the
electrolyte. Their output voltage is high enough that they will still
attempt to charge at nearly 1 A, even when the battery is fully charged.

A better choice is a regulated charger that will automatically switch to
a lower charging rate once the battery is fully charged. These chargers
start out with a high output voltage that will charge the battery at
around 1 or 1.5 A, but when the battery voltage rises far enough, will
automatically switch to a lower output voltage, which drops the charge
current to 0.1 A or less - just enough to overcome the self-discharge of
the battery without overcharging it. A couple of examples are the
Deltran "Battery Tender" and the Schumacher "Battery Companion". I have
a little more experience with the Deltran units, but I have also used
the Schumacher one, and both brands seem to do a good job of maintaining
flooded batteries without damaging them. The Deltran chargers seem to
be a little pricier and harder to find, but are available in 24 V. I
don't think the Schumachers are available in 24 V, but the 12 V ones are
less expensive than the Deltrans and are often available at Wal-Mart.

If I had to use an unregulated cheap "trickle charger" to maintain an
unattended battery for a long time, I would probably use it with an
electromechanical lamp timer to only run the charger for an hour or two
a day. This is enough time to correct any self-discharge, but not long
enough to overcharge the battery really badly. The electromechanical
lamp timer is so that it will pick up where it left off in case of a
power outage.

FWIW, in an older revision of their manual at
http://gillbatteries.com/images/sect4.pdf , Gill specifically said
"don't let a trickle charger run forever". The legal and marketing
departments got at the manual and turned it into
http://gillbatteries.com/battery_PDF...ice_manual.pdf
which still doesn't like trickle chargers, but you have to read between
the lines a bit.

Whatever you use, don't forget to unhook it before you fly off. OK,
you'd never do that, but... When I work on ground vehicles where I
might not be the next person to operate the vehicle, I have found the
most reliable way is to loop the extension cord for the charger through
the driver's door handle or steering wheel. Most people will try to
figure out what the cord is hooked up to before driving off. If you
have a lot of money, you can get a nifty flush-mount male 120 V plug
with a solenoid-operated ejector pin in it. The solenoid gets wired
to the vehicle electrical system, so when you turn on the key/master/
whatever, the solenoid comes on and spits the plug out of the socket.

Roger mentioned that he uses a heat lamp on his motor-generator battery
to keep it warm. Depending on the mounting of your aircraft battery,
you might be able to do something similar (with hardware you probably
already have) to decide if the "official" battery heater would help.
Calibrate your head with a few "start after cold soak" cycles with no
heater. Then get a drop light with a plain old incandescent bulb in
it and put it under the battery somewhere - watch out for things that
might melt, fluids that might drip on the lamp, etc - and switch it on.
Hang out for 30-60 minutes (don't run off), then take the drop light
out and try a start. If the engine seems to start a lot easier, it
might be worth spending money on the "official" battery heater with a
thermostat and everything.

A few years back, I put an oil pan heater on my Chevy. This was in
Kansas City, where you really don't need an oil pan heater, but when
I plugged it in, it did seem to make the engine start a little easier
after a cold soak. One winter, when I plugged it in, it made the engine
start a _lot_ easier after a cold soak - nearly to the point that if I
didn't plug it in I sometimes wondered if it would start or not. I
didn't figure it out right away, but the battery was crapping out -
later in the winter it died for good and I installed a new battery.
With the new battery, the engine started pretty easy whether I plugged
the heater in or not. The heater still made a difference, but not as
much as it did when the battery was on its way out. So I think in my
case the heater was useful, but not as useful as having a good battery.
If you live way up north, a good battery _and_ a heater may be more
useful.

Disclaimer: This is based on experience with flooded and VRLA/AGM
batteries for starting and traction on ground vehicles. I don't have
an A&P; I don't even have a TG&Y. I don't get money or other
consideration from any of the companies mentioned.

Matt Roberds