 We use batteries for just about everything in our lives. From our cell phone to our laptops, even a car runs on a 12V battery. Which provides enough power to its motor and other parts like the music system or head and tail lights. We have also seen and used these smaller batteries. These are called AA batteries and we use them in torches, glocks or even cameras. There is some difference between the battery of a car and these batteries. The difference lies in the chemistry behind them, but the main purpose still remains the same. They are used to provide enough power for the devices to work. And here's a wild question. Do you think it's possible to start a car, one that you can actually sit in and drive, using these simple household AA batteries like the ones that we see in torches and glocks? Well, the short answer is yes we can, it's possible. Let's see how. Now the motor that is used in the car is called a starter motor, it looks somewhat like this. And it draws a huge amount of current so that it can get the engine going. It draws on an average 250A of current and operates at 12V. This is a very high requirement of voltage and current. And AA batteries are usually rated at 1.5V and they have an internal resistance of again on an average 0.2 ohms. If you want to start a car using these, we would need a bunch of them. Since the AA battery has an internal resistance, the voltage drop across its terminals is called the terminal voltage and this is given by E-IR, where E is 1.5V, R here is the internal resistance. Now the battery can provide a maximum of 7-8A of current, 7-8A of current can be drawn from the battery. But the battery may become extremely hot from doing this. And there is a possibility of the battery either venting a hot gas or the container exploding from the pressure buildup inside. So this is somewhat risky to do. So let's work with two amperes. Using two amperes is a lot of current, but let's say that we want two amperes to be drawn from the battery and then let's try to get a sense of how many of these batteries would we need in that case. So if two amperes of current is flowing over here, the terminal voltage would be, this over here is 1.5, minus 2 into 0.2 and this comes out to be equal to 1.1V. So this AA battery will supply a voltage of 1.1V when two amperes of current is being drawn from it. But the motor requires 12V. So to meet the voltage requirement of the motor, we would need to put a bunch of these batteries in series because voltage gets added up in series, right? Let's see how many of these would we need to connect in series. The voltage requirement is 12V and one battery is providing 1.1. So 12 divided by 1.1. This comes out to be approximately equal to 11. So we would need to place 11 AA batteries in series and only then we will be able to meet the voltage requirement of 12V. So let's do that and see how it looks. We have 11 AA batteries in series and we meet the voltage requirement by connecting them in series. But the current is still two amperes. We haven't met the current requirement. The current requirement is 250 amperes and two amperes of current would be flowing in this string of series connected batteries. So if we have 125 of such series connected batteries in parallel to each other then the current in each branch would be two amperes and the total current would come out to be as 250 amperes meeting the current requirement. So we would need to add more batteries in parallel to form a series parallel or a mixed combination and we can connect them to each other to form the entire circuit. This means that the total number of AA batteries for starting a car would be 125, 125 x 11 and this is 1375 number of batteries. We can start the car with even more or less than 1375 batteries. This is not a fixed number. If we want much less current to be drawn from the batteries, we would need more of these thousands more. And if we want less number of batteries, more current will have to be drawn from each, but that involves a lot of risk. So these batteries will be drained very soon and some of them are rechargeable, some aren't. But the idea of connecting them in series, in series to meet the high voltage requirement and connecting them in parallel to meet the high current requirement is followed even in the battery packs used in electric cars such as those made by Tesla. Batteries that are used in Tesla, however, have a very high voltage rating and can be recharged but they are also connected in a mixed combination, both in series and parallel to meet the voltage and the current requirements.