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OK you might be saying to yourself "huh"? But it is a number you can put to great use, especially as a barometer to tell you are on borrowed time and won't be long till you are replacing batteries. But this thread is all about me. 
Basically a call to post your batteries internal resistance for me to crunch data. It will not take long measure it, nor is it difficult requiring a lot of test equipment, just a couple of simple steps. What you get out of it is priceless.
So here is how you do this.
1. First you want the batteries to be at or near 100% charged up, anything above 90% is good and rested a bit if possible.
2. Turn off all loads so there is ZERO current flowing and panels are off like just after sunset. Once you are sure the system is dead, measure and record the battery voltage right on the battery positive and negative post. Monitor for a minute or so until it stabilizes. Label this voltage as V1
3. Now leaving your meter connected to the battery turn on all the load devices you can without over loading anything.
4. This maybe the show stopper for most of you, but note and record the current with everything turned on.
6. Simultaneously while you record current, note loaded voltage on battery and record that voltage. Label current as Il, and voltage as V2
7. Test concluded, put everything back to normal.
OK to find your battery or batteries internal resistance we use the data you collected. Ri = [V1-V2] / Il
So let's run through an example. 12 volt system loaded with 40 amps. Open circuit battery voltage or V1 = 12.5 volts, Loaded voltage or V2 = 11.86 volts. So Ri = [12.5 - 11.86] / 40 = .016 Ohms.
How do you use that number? It works best on brand new batteries to establish a Base Line, but still useful on older batteries. When you start noting the Ri is growing means you have lost capacity and the batteries are on there way out.
Basically a call to post your batteries internal resistance for me to crunch data. It will not take long measure it, nor is it difficult requiring a lot of test equipment, just a couple of simple steps. What you get out of it is priceless.
So here is how you do this.
1. First you want the batteries to be at or near 100% charged up, anything above 90% is good and rested a bit if possible.
2. Turn off all loads so there is ZERO current flowing and panels are off like just after sunset. Once you are sure the system is dead, measure and record the battery voltage right on the battery positive and negative post. Monitor for a minute or so until it stabilizes. Label this voltage as V1
3. Now leaving your meter connected to the battery turn on all the load devices you can without over loading anything.
4. This maybe the show stopper for most of you, but note and record the current with everything turned on.
6. Simultaneously while you record current, note loaded voltage on battery and record that voltage. Label current as Il, and voltage as V2
7. Test concluded, put everything back to normal.
OK to find your battery or batteries internal resistance we use the data you collected. Ri = [V1-V2] / Il
So let's run through an example. 12 volt system loaded with 40 amps. Open circuit battery voltage or V1 = 12.5 volts, Loaded voltage or V2 = 11.86 volts. So Ri = [12.5 - 11.86] / 40 = .016 Ohms.
How do you use that number? It works best on brand new batteries to establish a Base Line, but still useful on older batteries. When you start noting the Ri is growing means you have lost capacity and the batteries are on there way out.
Then again, perhaps they act differently with large lead acid batteries - I don't know. I do know that the Junsi iChargers don't require a deep discharge to measure Ri. Food for thought for those who want to use these to baseline their Ri.
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