I was posed the question of whether or not you would be able to start a car with 8 small 1.5V batteries in series (thereby creating the required 12V most cars run on). I immediately answered "no", with my reasoning being that the small AA batteries would not be able to supply enough current for the car.
Although I know this to be true, I have been thinking more and more about the reason behind this. Although there are many factors involved, would it be correct to say that the main determining factor for a battery's "current pushing ability" is its internal resistance?
My reasoning behind this is that, when the internal resistance of the battery is relatively high, and due to ohms law where I = V / R, the resistance of the battery will play a greater role in determining the current pull at low load resistances, but not much of a role at high load resistances?
This also makes sense to me, as it seems like car batteries tend to have internal resistances of many magnitudes smaller than tiny AA batteries.
Best Answer
Short answer, yes you are right. The Ri of a battery limits the current it can supply, but the Ri is not the real cause, more a symptom. The design and characteristics of the electrodes, chemical processes, temperature, etc. all kinds of internal and external parameters interact when current is "requested" and Ri is just your way to put all these influences into one handy value. And we need to mention: Ri changes while the battery operates.
For example, my 50km/h RC car does not move a mm when the LiPos are 0°C or below. Temperature is a huge influence on Ri. In the summer 2 of these packs should start my car easily.