Testing batteries with loss of power

Yesterday, we lost power for approximately 7 hours. When I got home, power was still off, but alarm was functioning. so i tested the voltage on my batteries to see how they were doing. I had 12.7V on my 12A battery, and 12.06V on my 8A battery. That is seems pretty good. Of course, in alarm, it would probably go down much faster.
 
I was wondering if anyone had any input on battery length of operation.

Elk makes a battery tester that will test the potential for the battery, not just voltage. 
 
When my Altronix PSU didnt come back online to AC power it dragged the 12V batteries down to 8.5V (no low battery cutoff built into it).  I charged the batteries with an external 12V charger and they got back up to 12V, but when the Elk battery tester was hooked up to to them it showed they were clearly damaged by the ordeal.  Probably about half of the potential runtime compared to my undamaged 12V batteries.  But just looking at the voltage you would have no idea.
 
Since the batteries are supposed to be tested fairly regularly, investing in the battery tester might not be that bad an idea.
 
Which reminds me, I need to order replacement batteries and the low battery disconnect module for my Altronix PSU

I saw that tester. But I was avoiding buying a tool just for this purpose. Do you know if this can be used to test car batteries as well? Or is there a tester that could be used to test different types of batteries?
 
How much is the Elk tester?

newalarm said:

I saw that tester. But I was avoiding buying a tool just for this purpose. Do you know if this can be used to test car batteries as well? Or is there a tester that could be used to test different types of batteries?
 
How much is the Elk tester?

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I saw on on Ebay a while ago for around 100 (it was used).  new it looks to be about 175 or so
 
The manual doesnt outright say it can be used for car batteries but it does refer to a FAQ of "testing cold cranking amps".  The answer is that it cant measure CCA, but it doesnt say you CANT use it on a car battery.  The specs say its for any 12V rechargable battery, not sure if that means car type batteries as well.  Im sure an email to Elk would get you an answer.  If it can be used on car batteries it definitely improves the usefulness. 
 
You could know well ahead of time if you will end up stranded because of a bad battery (oddly enough I barely made it back from an out of state vacation, because the wifes car battery was just about dead while we were down there)

For those that can't justify buying something like the elk tester it can be done with a few power resistors and a multimeter.  Just google 'measure battery internal resistance'.  Elk measures mhos which is just 1/resistance.  Here's one link:
 
http://laserpointerforums.com/f67/how-healthy-your-batteries-how-measure-internal-resistance-57576.html

Thanks, that is helpful. I may try that.

newalarm said:

Yesterday, we lost power for approximately 7 hours. When I got home, power was still off, but alarm was functioning. so i tested the voltage on my batteries to see how they were doing. I had 12.7V on my 12A battery, and 12.06V on my 8A battery. That is seems pretty good. Of course, in alarm, it would probably go down much faster.
 
I was wondering if anyone had any input on battery length of operation.

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Any reasonable quality load tester can be used to test your batteries. You can even use a cheap carbon pile tester from HF if thats the route you wish to take.
 
With respect to your 8 AH battery being at 12.06 volts.
 
At that level the battery is at 50% capacity. Anything above 12.60 volts is aprox 100% SOC. For the typical SLA flooded battery initial voltage is 12.8 to 12.98 SOC but keep in mind these are high output APC batteries.
 
By default the system should be performing a load test on the batteries. In the real world you should be performing a live load test to ensure the system actually operates and provides the stated run time.
 
Teken . . .