a 30Ah 12V hawker is about 200, maybe $250.
half a bank, of them is 100 for the capcity dobled for the voltage,
or, 200. 20,000/200 is about $100 a battery, which is the cheap side,
even taking into accont bulk-buying. thats only slightly more than the
low-end yuasa's, and then you have to build the bank, and transport
etc.

Actually, i use the hawkers mainly in electric vehicles. Part of my
job involves building and testing automotive-type electrical systems,
and i usea hawker till its flat, and charge, or at least untli i've
finished the day, then top up.

I know British telecom also use them for emergency power systems, and
for portable emergency power packs - and if you've ever seen BT's
infrastructure, you'll understand why they don't skimp on the
batteries.

More expensive than the Hawkers, I suspect - they're GNB Absolyte batteries.
The small banks run $5000 US, while the larger banks are $20 thousand. The
large bank I mentioned was half a 3000 AH 48V bank. They look like
http://www.batterypowersystems.com/products/absolyteIIP.htm .

The likely difference in failure modes is because of the type of service. In
communication service, the batteries are "floated" at 2.25 volts per cell by
fixed voltage, current limited chargers. In automotive use the charge is
more intermittent, so thermal runaway is rare. However, the batteries are
much smaller so the thermal mass is smaller. A battery that did fine on
in-town trips is really tested on long trips, where the charging is constant
enough to possibly trigger thermal runaway.

But I suspect the design is different enough that the car batteries fail
through dehydration most of the time. Our Toyota Prius has a sealed
lead-acid aux battery... reports from people who've had to replace them are
very familiar. They let it run down, charged it by jumping and letting the
car charge it, often in warm weather. Sealed batteries are still the old
gell cells with minor updates. As long as they aren't in the engine
compartment they aren't too bad.

Mike

sounds like you're using cheap ones. yuasa, powersonic, or similar?
those i'd expect, they're prety low quality ones. Personally, i'll
always use hawkers - never had a single runaway, explosion or other
problem. Had to deal with lots of the cheaper ones exploding, and
catching fire before, but in similar situations the hawkers have
swelled, and thats about it. There's a reason yuasas and such aren't
certified safe for air travel, and hawkers are.

Unless I'm mistaken, all sealed lead-acid batteries are recombination with
overpresure vents, also known as Valve Regulated Lead Acid (VRLA) batteries.

There are different grid chemistries, though. I assume the automotive types
are designed for higher temperatures and non-deep cycle. We use absorbed
electrolyte VRLAs where I work (communication sites) and they are spec'd at
15 or 20 years life, depending on the specific model. We started using them
because they have a smaller floor area for the capacity than flooded cells
and because they don't need venting to the outside or other safety
precautions. They have been very tempramental, though, and we have not had
one last ten years yet. They all die the same way, and the process was
described to me by a friend who worked for ABB selling the things. As they
age, the leakage current for a given temperature creeps up. At some point,
either because of A/C failure or just because the critical temperature
dropped to room temperature, the battery will go into thermal runaway. The
leakage current will rise, heating the battery and increasing the leakage
and further heating the battery. A couple weeks ago I caught one of our
banks at 120 degrees F and consuming 1500 watts... because somebody left the
room door open for a few hours. $20K will fix it up just fine, though. The
highest temperature we've recorded was 191F, and the tech felt the heat on
his face when he entered the room. Around 220F the polypropylene cases
soften and the batteries explode like small bombs - I've seen a picture of a
room full of equipment that was splattered with boiling acid that way.

The demise in automotive use should be different because a charger isn't on
it 24/7. Higher temperatures during charging cause the battery to vent,
losing the vented vapor forever. Eventually, the lost water causes the
battery to dry up and the output current and capacity to drop - the way gell
cells (and that's what all VRLA batteries are, after all) have died for
decades. A whole lot better than going supernova!

Mike

Depends on the type of sealed battery. My preference is for a sealled
gas recombination based one, with gas vent - they don't explode at
all, don't even leak fluid. Used to run them all day long in a big
plastic greenhouse, lit by some 40KW of lighting, inside an old WW2
building, with the outside temp in the 110's - not a single
roble,.Course, at $300-ish a shot for a reletively small 30Ah one,
they're not cheap, but worth it - especially since they'll do about
2000A peak output, and will take the same input as charge.

My car didn't have A/C but had short battery life the same as my wife's. Two
years, then replace (and that was with batteries advertised as being
designed for hot climates). On hot afternoons the temp guage would already
be off the bottom peg before I ever started the engine. The day it was 122,
when I started my car the battery simply exploded.

I also buy only full-service batteries. Sealed batteries in that heat are a
bad idea, and I just carry on the tradition here.

Mike

Batteries are not engine componants, they work by time, and not miles.
Was the battery topped up?

Did you let the car run for a little before turning the AC on, and
similarly turn the AC off a little bit before you turned the engine
off in Az? if not, thats what would have killed them.

Yes and no. The battery is designed to be chargable. using, and
draining and charging the battery doesn't 'damage it' per se. If it is
kept below 10V for an extended period of time (say 12 hours or more)
then it is irreperably damaged. using a trickle charger is the best
way to charge a low battery.

That really depends on the climate. When I lived in Phoenix I never had a
battery survive three summers - they would almost always give up early in
the third summer (like around May, since summer there is pretty much
May-September, and it's hit 100 degrees in March.) Now I live in Flagstaff
and the only battery I've had to replace in 4 years was in a car we had
recently bought.

Other things can suck the life out of a battery, especially if they are run
down and charged by driving the car.

Mike

Hello,
Recently went in for an oil change at 35K.
The battery load test failed on my car even
though I appear to have no starting problems.

My questions:
Besides the honda battery (delphi), are there
other good replacement batteries?

I'm looking at:
Everready (by AC delco) $65
Energizer               $60
Bosch                   $79
Diehard                 $79    (Sears)

Is it normal for the battery to fail load test
at only 36K?

THANK YOU!