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.