Batteries in Series: Getting the Hook-Up

If you're a new EV driver and you don't know your batteries in series from batteries in parallel, no worries. No matter what kind of electric car you drive - be it a Zenn from the dealership or a conversion - someday, you're going to need to change your batteries. You gotta get them hooked up right.

Here's the problem, and it's a math problem: Batteries come in 6, 8, or 12 volt packages. Your car's system is 120 volts (or whatever). So how do you get from, say, 6 volt batteries to a 120 volt car?

If you converted your car, you already know the math bit, because it was in the conversion manual you bought: To add voltage, wire your batteries in a series configuration. 120 divided by 6...that'll be 20 batteries in series. Right?

But what does that mean?

You'll have your batteries sitting in a battery box. You might have more than one battery box in your car in order to distribute the weight evenly - doesn't matter for purposes of wiring your batteries in series.

Start at one end of the batteries...

Start at one end, and connect the positive post of the first battery with the negative post of the second.

Connect the positive post of the second with the negative post of the third. Repeat the process until you get to the end.

When you get to the end, you'll have a positive post left over at the twentieth battery, and a negative post at the first. They will be attached to the load.

If you're connecting batteries in series, it is important to make sure that each battery has the same capacity - meaning, the same amp-hour (AH) rating. If some of your batteries have 180 AH, and others 220 AH, the batteries in the series with fewer amp hours will discharge too deeply, shortening their life. Dramatically.

So what if I need more amp-hours?

Suppose you had a battery with 6 volts, but only 10 amp-hours? Could you wire several of them together to give you more running time?

Yes, actually, you can.

If you need more amp hours, you can wire several batteries together in a parallel configuration. This means you hook the positive post of the first battery to the positive post of the second, and the positive post of the third, and so on...and the negative posts in the same way. If you hooked 20 6v, 10 AH batteries together in parallel, you'd end up with 6 volts, and 200 amp hours. Fortunately, several battery makers already sell this battery pre-made, so you don't have to do that!

If you're connecting batteries in parallel, it is important to make sure that each of the batteries in the configuration has the same voltage.

Can I have batteries in parallel and batteries in series?

Yeah. But most of the time this won't be necessary. Why? Because you can just purchase your batteries with the right number of amp hours, then connect the batteries in series. I suppose you could wire the parallel units together first, then connect those groups into a series...and people do this, especially with small lithium ion batteries...but personally, if I could avoid it, I would.

One more thing about those connectors...

You'll need connectors that have thick enough wire to carry the necessary amount of current, or they'll heat up.