On 11/27/2014 12:42 PM, trader_4 wrote:
On Wednesday, November 26, 2014 10:00:42 PM UTC-5, mike wrote:
On 11/26/2014 2:31 PM, Tony Hwang wrote:
Percival P. Cassidy wrote:
On 11/26/2014 09:30 AM, KenK wrote:

While trying to come up with something more to worry about, I thought
of my
backup battery. I have a 12 v deep discharge lead acid battery with a
Battery Tender wall wart charger. I check the battery water level
monthly
(usually) and keep an eye on the charger indicator light. I see no
problems
but wonder if there was an easy way to be sure the battery will be
charged
when the power goes out and I need it for a light and, if summer, a fan.
Just trust the charger to detect a problem and warn me by changing the
light color or blinking? An easy test of some sort, other than turning
the
light and fan on for a half day or so every few months?

I can't think of anything (worth the cost) that's easier to do or more
accurate.
Does the battery do what you want when you ask it to do that?
Test doesn't get more relevant than that.


Yes that's the best test. But the only way he'll know that is to
put his load on it and see if it lasts the expected number of hours.
I guess doing that once a year isn't a bad idea. But if you do it
regularly, every cycle takes more life out of the battery. A battery
tester can test it with a short duration load.



Never ask a question if the answer won't change the future.
In this case, if you run some "test", what are you gonna do with the answer?


Presumably he'd replace the battery if it's no longer adequate.


If the light doesn't work, you have a clear definitive answer and
you know exactly what to do...go buy a new battery.


Only if the light doesn't work after X hours. A mostly bad battery
could still light up the light for a brief test and he wouldn't know
if it was capable of going the normal length of time in an outage.

I can't say you're wrong...just that you're overthinking it.
We don't know the whole story, and you can come up with a counterexample
to prove any definitive statement wrong.

I believe there are battery testers that can tell you a lot about the
condition of a battery, but are they "worth the cost" in this situation.

Applying some logic...

What is "no longer adequate"?
What's the calamity that ensues if the light lasts x-1 hours? x-2 hours?
x-3 hours? At what point does the cost of some possible future calamity
exceed the current cost of a new battery?

If it's a life-support situation, you replace the battery on a schedule
and have an additional battery on standby.

If you used the system frequently, you wouldn't need to test it.
In particular, a yearly test suggests that it's more than a year
between power outages.

What's the cost, in additional battery degradation due to discharge, of
20 partial
discharges over the next 20 years? You don't need to run it flat to
learn that it's degrading. Measure the voltage, under load, after an
hour and graph the number.

And the system test is of the whole system
including source, load, wiring, switches, etc.

I have a UPS on my computer.
The battery is not new.
Runs for about 5 minutes.

Power outages around here are of two types.
Virtually all last less than a second.
The rest last for hours.

Replacing the battery with one that runs 10x as long
would be of zero benefit.

My first line of defense in a power outage is the nap.
Nothing fixes a power outage faster than a long nap.

Second line is two dozen harbor freight free flashlights.

Next is the 12V battery-in-a-box car starting gizmo.
Then the car battery.
Then the 500W generator.
Then, if it's cold and I need to keep the pipes from
freezing, I need to run the furnace off the 2KW generator.
Then, if I need to power my neighbor's freezers to keep
his food from spoiling, I run the 6KW generator.

Can't remember the last time I needed more than the nap
and one flashlight. My only excuse is that I acquired all
this stuff over 40 years at pennies on the dollar.

Managing expectations is far easier than obsessing over
attempting to
maintain your full existence during a power outage.

Harbor Freight will sell you a generator for
$67 after 25% coupon that will provide REAL backup power if ever needed.
And that's probably in line with what you'd pay for a new
battery.