Rising Internal Resistance

High battery capacity is of limited use if the pack cannot deliver the stored energy effectively. To supply power, the battery needs low internal resistance. Measured in milliohms (mΩ), resistance is the gatekeeper of the battery; the lower the resistance, the less restriction the pack encounters. This is especially important on heavy loads such as power tools and electric powertrains. High resistance causes the voltage to collapse on a load, triggering an early shutdown. Figure 1 illustrates low and high resistance batteries in the form of free-flowing and restricted taps.

Lead acid has a very low internal resistance, and the battery responds well to high current bursts that last for a few seconds. Due to inherent sluggishness, however, lead acid does not perform well on a sustained high current discharge and the battery needs a rest to recover. Sulfation and grid corrosion are the main contributor to the rise of the internal resistance. Temperature also affects the resistance; heat lowers it and cold raises it. Heating the battery will momentarily lower the internal resistance to provide extra run time.

Alkaline, carbon-zinc and other primary batteries have a relatively high internal resistance, and this limits its use to low-current applications such as flashlights, remote controls, portable entertainment devices and kitchen clocks. As these batteries discharge, the resistance increases further. This explains the relative short runtime when using alkaline cells in digital cameras. 

Comments

On December 12, 2011 at 10:16am

Guillaume wrote:

If anyone could provide me with a link of a lead-acid battery internal resistance vs temperature, it would be awesome.

On December 13, 2011 at 6:37am

girish yadav wrote:

lead acid battery performs better at low intl resistance at low temperrature intl resistance rises while at higher temperature vice-versa.

On December 13, 2011 at 12:40pm

Guillaume wrote:

@girish

I should have been more explicite in my question. I already knew that a colder temperature meant a higher internal resistance (yeah, I know I should have mentionned it).

What I would like to know is by how much the internal resistance is affected by a change of temperature. For instance, take the internal resistance of a battery at 30°C (say 4mH).

What will it be at -40°C ? 2 times 4mH ? more than that ?

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