Batteries: Safety, Placement, and Cycle Life

by Judy
(Astoria)



Say I was to convert a Honda Civic 4-door to electric. I have two children to transport to school on my commute. Would they be sitting on top of or right in front of the lead-acid batteries in the car?

Also, I noticed in the battery information they mention Cycles (750 or 650). Can you translate that into miles or number of months for those of us less familiar with this technology?

Hi, Judy -
The best place to put battery boxes is outside the passenger cabin, evenly distributed, and low. You'll have somewhere in the neighborhood of 20 heavy batteries in your car, and they'll need to be somewhere accessible (for service, for charging, for changing out). Something to think about!

A small car conversion makes this a bit of a challenge, and a lot of folks end up taking out the back seat altogether and putting battery boxes where the seats used to be. There are other options, though. I've seen people put a lot of the batteries under the hood, and in the trunk. They don't have to be right under the kids.

I feel obligated to point out, however, that as of right now, your Accord's gas tank is right under your kids, and has a lot more lethal potential than a battery pack. We've all gotten so used to this danger that we tend to forget about it.

Now, on the battery cycles question.

In the book, "Build Your Own Electric Vehicle" by Seth Leitman (page 189), it talks about battery cycle life, saying that the number of cycles you will get out of your battery pack ultimately depends on you and your EV application.

I've heard people say that the number of cycles is absolute; it doesn't matter whether you discharge them 50% or 90%, a cycle is a cycle. This doesn't sound right to me, and in fact, isn't right.

The equation, according to Leitman's book, is actually battery life cycles = k/depth of discharge.

K depends on your driving needs and habits, and is different for every EV driver.

What does this mean in English?

If you discharge them very deeply, you'll get fewer charge/discharge cycles. Discharge them lightly and keep topped up with charge, and you'll get more cycles.

Do you drive your car every day? Then, depending on how much you drive, you might consider one day a "cycle".

Batteries need to be fresh, not sitting around a warehouse for a year before you get them. They need to be charged gently. Kept warm, but not too warm. Discharged gently, and not too deeply.

No wonder Chevy refers to the Volt's battery pack as "the Diva"!

All the best -
Lynne



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