Mygreenwheels

For ages I’ve been trying to find a simple introduction to batteries for EVs. Perhaps there is one out there, but I haven’t come across it.

I don’t want something so technical that I can build my own car battery in my garage. What I do want is something which explains to me in fairly simple terms how batteries work and, more importantly, what the shortcomings are that prevent all modern cars from being electric.

So, what I’ve decided to do is post something and ask for contributions. If I’m wrong let me know. If I’ve over-simplified to the point of inaccuracy post an addition.

Maybe at the end of it I’ll then be able to explain what the situation really is when people say to me: “Electric cars? Nice idea, but the battery technology isn’t going to be available for years.” They don’t really know, but neither do I.

I’ve decided to write this in a question and answer format. Feel free to add to it using the comments section at the bottom of the article. This is very much a work in progress.

What do people mean by a "car battery"?

Almost always this is a lead-acid battery. It contains plates of lead and lead oxide. These plates are submerged in a solution of 35% sulphuric acid and 65% water. The process causes a chemical reaction releasing electrons that flow through conductors producing electricity.

Interesting fact: What is thought to be the world’s oldest battery comes from near Baghdad. It was discovered in 1938 and is between 1,500 and 2,250 years old. Nobody is sure, but it seems to have been used for electroplating rather than powering an electric chariot.

Why can’t you use a load of ordinary car batteries to power an electric vehicle (EV)?

Although lead-acid batteries all work in roughly the same way there are variations. The plates vary in thickness and how porous they are. They also use a variety of alloys including calcium, cadmium or strontium.

The main breakdown is between the starter batteries used by petrol-engined vehicles to give a quick burst of power to start the internal combustion engine and “deep cycle batteries” which are designed to provide sustained power over a longer period of time. The latter are used for EVs such as golf carts and also to store energy from devices such as wind turbines and solar panels.

So ordinary car batteries would in an EV wouldn’t last very long both in terms of daily mileage and before they had to be replaced.

What are the shortcomings of lead-acid batteries for electric cars and other EVs?

The main problem is the energy to weight ratio. Anything powered by lead-acid batteries has to pull along what are essentially boxes filled with lead and liquid as well as the weight of the vehicle itself. It’s not likely to be very efficient.

Additionally, lead-acid batteries don’t last for ever. A good quality ICE car battery will last for an average of about five years. A deep discharge battery in a golf cart can expect about the same lifespan. All types of lead-acid battery are affected by factors such as poor maintenance and extremes of heat and cold.

One sure way to reduce the life of a lead-acid battery is to charge it too fast. That’s why most electric cars need an overnight charge.

So why do most EVs still use lead-acid batteries?

The first point is it’s a tried-and-tested technology which has changed little in the last half-century. The batteries are more efficient and easier to maintain, but there haven’t been any revolutionary developments. That also means prices are relatively low.

Lead-acid batteries are also fairly efficient compared with some of their competitors. They give out around 75-85% of the energy that’s put in. There are, however, substantial differences according to the state of charge of the batteries.

Next I’ll be looking at some alternative batteries for electric vehicles.