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 suspect I'll just
have to take my chances.
You know it's time to clean the refrigerator
when something closes the door from the inside.
My experience, is that a Harbor Freight float
charger will "boil" the battery dry, and kill
it. I'd suggest to put your float charger on
a lamp timer, and only run the charger an hour
or so a day. Or once a week for a couple hours.
You can get a hydrometer, from the auto parts
store, if you want some thing else to check.
The real life action test is the only way to know.
I'd also use a volt meter, and do some research
online. A lead acid battery won't recover from
a total discharge, there is some voltage not to
go below that point.
I have a solar charger going set at 13.8 volts with temperature monitoring.
I checked the cells, and still see correct levels. It's been going for two
It's probably best to discharge at intervals to equalize the cells.
The hf float charger does deliver too much current as you say.
1) You should not be charging a "wet" type lead acid battery in-doors,
the hydrogen emission is explosive. The type of battery you should be
using in your house would be VLRA. (Valve regulated lead acid.)
2) Since most people ignore my first point when I warn them, the type of
charger you use /can/ make a difference. Ideally you'd want to employ
hysteresis-loop charing techniques. This type of charger only charges
between preset voltage ranges and minimizes water consumption and
maximizes battery life. You are unlikely to find such a charger in the
"consumer" market...so the next best thing is a "float" charger which
will retain a constant voltage just below the battery's gassing point.
What you do not want is a "trickle" charger. That type simply puts out
an /unregulated/ small amount of current.
3) There are testers that can check a battery's internal resistance
without actually putting a load on it. They are fairly reliable but the
only sure way is to actually load it down. A reasonable test would be to
simply place a heavier than usual load on it for a relatively short
period of time and check the voltage drop. If the battery can stay above
11 volts under a heavy load it's probably fine.
Additionally: If you do insist on using a "wet" type battery my advice
would be to /not/ keep it on charge. Unless there is a load on it, it
may only require a "top off" every three months or so. The charging area
should be well vented.
I worked for Enersys as a Senior Service Engineer & retired after 38
years. Many a time have I seen exploded batteries and I did so myself
The one exploded battery I've known in person was
an old farmer trying to start a Gehl Skid Steer.
He had the battery on 12 volt boost. He went to
adjust the battery clamps with the charger still
on / plugged in. I was on the other side of the
machine, but I remember his words "get some water
for my eyes".
The Op's float charger won't make enough hydrogen
to do that.
Christopher A. Young
Learn about Jesus
good point about indoors vs outdoors. I had a battery explode INSIDE my
car's engine compartment. I stupidly left the contacts loose and enough
gas enough spark and the battery became non-existant with acid washing the
interior of the engine compartment!
Why not on a really small trickle charge say 100mA, or 10mA, or 1mA, or
whatever it takes to sustain the voltage? ignoring temperature.
The problem with a trickle charger is that it simply puts out a small
but unregulated amount of current. In the probable event that it's
output would be slightly higher than the battery's idle discharge rate,
the voltage could go above the battery gassing point. Not only will this
use up water, it will be putting out hydrogen.
Plus, if the battery was discharged, a trickle charger would take
"forever" to recharge the battery.
Most chargers are regulated to prevent excess gassing and some are even
Except for all the batteries that I have in UPS's I never keep any of my
extra batteries on charge. They are kept in a cool location and some are
only "topped off" twice a year.
I have a couple of rarely used 6V gel cells that are over 20 years old.
One is low capacity but usable but the other still has decent capacity.
Had the batteries been kept on float charge they would not have lasted
more than 4 or 5 years.
And add the IQ4 smart-charge module.
Connect an el-cheapo multimeter (Hazard Fraught or the like) across the
terminals (permanently) but turn it on only to check the voltage from
time to time.
I can't think of anything (worth the cost) that's easier to do or more
Does the battery do what you want when you ask it to do that?
Test doesn't get more relevant than that.
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?
If the light doesn't work, you have a clear definitive answer and
you know exactly what to do...go buy a new battery.
I suspect I'll
On Wednesday, November 26, 2014 10:00:42 PM UTC-5, mike wrote:
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.
Presumably he'd replace the battery if it's no longer adequate.
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
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
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
On Thursday, November 27, 2014 6:43:40 PM UTC-5, mike wrote:
All I can do is give options that answer the question.
IDK what the value is to the OP of being
able to test his battery. It's up to him to figure that out and how much
a battery tester would cost and how a battery tester fits his requirements
versus the putting it through a full cycle test periodically method.
There are also options from buying a new battery tester to buying a used one
on Ebay. Presumably, the OP, if interested, can research that and figure it
out. Someone even pointed out that some multimeters have a battery load test
function. I've never seen one, but if they do, then maybe he doesn't have
a multimeter, could use one for other purposes too, and that option would
work for him.
As to overthinking it, IDK exactly what you mean. You suggested that the
best way to test it is to actually make it do what you expect it to do,
periodically. All I did was point out that to do that, you'd have to
put it through a typical full usage cycle, or at least close to it, and
that each time you do that, it lessens the life of the battery. I also
said if you do that once a year or so, and that's adequate, it should be
We don't know because that was never given. What the parameters are
and how you can test to those parameters are two different things.
And I'm the one that's overthinking things?
That's what a battery tester will do in seconds. Maybe he wants to buy
one of those instead? Anything wrong with that?
The rest of the system can be checked with high accuracy in just
a few seconds, by turning it on. That isn't the case with a battery,
unless you have a load tester.
Irrelevant because your requirements and priorities <> OP or others.
And I thought the question was about how to test a battery.....
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