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Ever notice some batteries have capacity at top, others at bottom ?

OnTheRoadAgain

Solar Enthusiast
Joined
Feb 22, 2021
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I have noticed that some batteries have greater capacity at higher voltage while other have all their capacity at lower voltage.
in this example I'm speaking of lead acid batteries.

I have a somewhat fancy (Chinese) DL24P Capacity tester to check battery capacity.
Some lead acid batteries will stay above 12v for a long time during discharge then discharge more rapidly as the voltage falls below 12v for example.

Another battery will quickly drop from the 12.8v fully charged state to a lower voltage such as 11.7v and stay in the 11v range for a long time giving most of it's capacity below 12v.

Does anyone know WHY some batteries seem to have their capacity at higher voltages and others at lower voltage ranges?

The two graphs below illustrate this.
In the first graph, the voltage hangs high longer then drops faster under 12.5 volts.
BatteryCapacityGraph_2.jpg


In this graph, the voltage drops quickly to 11.3 volts then discharges more slowly.

BatteryCapacityGraph_1.jpg
 
I suspect it has more to do with Puekerts Law. Is there a current difference in those tests? That does not look like a complete discharge test which I am familiar with. What is the scale at the bottom? Amphours?
Ten years ago I switched to Lithium and don't have that problem.
 
Those graphs are for illustration purposes only and are not from actual data.

Internal resistance. I forgot about that. Good point. I'll check them both.
 
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