Internal Resistance of a Lead Battery

anhtho

Anyone knows what is the approx. internal resistance of a lead battery, say, 12V, 20Ah.
Thanks

Crosstalk

Lead acid batteries typically have an internal resistance around 20 milliohms.

anhtho

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).

Crosstalk

I'm not 100% sure on this, but I don't think that the battery's capacity matters.

nsaspook

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.

anhtho

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

nsaspook

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/po..._11_Jan_12.pdf
3 milliohm 140Ah: http://www.power-sonic.com/images/po..._11_Feb_21.pdf
5 milliohm 154Ah: http://www.power-sonic.com/images/po..._12_July_2.pdf

anhtho

Hi nsaspook, I agree that it depends on many other factors, and Ah capacity is the most important.
Thanks for the documents.