Internal Resistance of a Lead Battery

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Discussion Overview

The discussion revolves around the internal resistance of lead-acid batteries, specifically focusing on a 12V, 20Ah battery. Participants explore how internal resistance may vary with battery capacity and other influencing factors.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the approximate internal resistance of a 12V, 20Ah lead-acid battery.
  • Another participant suggests that lead-acid batteries typically have an internal resistance around 20 milliohms.
  • A follow-up question seeks clarification on what "typical" means in terms of battery capacity (20, 40, or 100Ah).
  • Some participants express uncertainty about whether battery capacity affects internal resistance.
  • One participant notes that internal resistance changes with battery age and state of charge, and that battery construction influences internal resistance, with AGM batteries having lower resistance compared to Gel cells.
  • Another participant argues that higher capacity batteries may have larger electrode plates, potentially leading to lower internal resistance, but acknowledges that total ionic resistance is influenced by multiple factors.
  • Links to documents providing specific internal resistance values for different sealed valve regulated battery types are shared.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between battery capacity and internal resistance, with no consensus reached on the matter.

Contextual Notes

Factors such as electrolyte conductivity, separator ionic resistance, ion mobility, and electrode surface area are mentioned as influencing internal resistance, indicating a complex interplay of variables.

anhtho
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Anyone knows what is the approx. internal resistance of a lead battery, say, 12V, 20Ah.
Thanks
 
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Lead acid batteries typically have an internal resistance around 20 milliohms.
 
Thanks Crosstalk for replying me.
You said 20 mOhms for a typical lead acid battery. But what is the typical ? 20, 40 or 100Ah ? (12V).
 
I'm not 100% sure on this, but I don't think that the battery's capacity matters.
 
Measurement of Internal Resistance: This is a for smaller cells but the principle is the same for "a typical lead acid battery". The IR changes as the battery ages and with State of Charge.
http://data.energizer.com/PDFs/BatteryIR.pdf
The battery construction (for Lead-Acid) affects IR, with AGM batteries having the lowest IR and Gel cells usually the highest for the same Ah rating.
 
Crosstalk said:
I'm not 100% sure on this, but I don't think that the battery's capacity matters.

I just think that the higher the capacity, the bigger the electrode plates, so the internal resistance should be smaller.
 
anhtho said:
I just think that the higher the capacity, the bigger the electrode plates, so the internal resistance should be smaller.

That's mainly true for the same type of battery construction but the total ionic resistance is a combination of factors like electrolyte conductivity, separator ionic resistance, ion mobility and electrode surface area.

Values for several different sealed valve regulated types.
3 milliohm 226Ah: http://www.power-sonic.com/images/powersonic/sla_batteries/pg_series/PG-12V200_11_Jan_12.pdf
3 milliohm 140Ah: http://www.power-sonic.com/images/powersonic/sla_batteries/ps_psg_series/12volt/PS-121400FR_11_Feb_21.pdf
5 milliohm 154Ah: http://www.power-sonic.com/images/powersonic/Info%20for%20PHR%20section%20of%20website%2011%20Nov%2015/PHR-12500_12_July_2.pdf
 
Last edited by a moderator:
Hi nsaspook, I agree that it depends on many other factors, and Ah capacity is the most important.
Thanks for the documents.
 

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