Rechargeable Batteries (Part 3)

By , February 4, 2015

This essay continues a series of posts on rechargeable batteries, beginning with Rechargeable Batteries (Part 1).

For the moment, we use two types of rechargeable batteries on our “homestead”: Nickel Cadmium (NiCad and )Nickel Metal Hydride (NiMH). These are the most common rechargeables available today.

NiCad’s main advantage comes from the nature of the electrical charge they hold: it lasts a long time if a charged battery goes unused. This characteristic allows us to charge up our NiCads when we have good charging days, and store them until needed.

On the down side, the cadmium in NiCads makes them toxic like alkalyne batteries, so they must be recycled or disposed of carefully.

Also, NiCads develop “memory”. This means that if a charged NiCad gets drawn down a portion of the total charge very many times, it will only charge to that level. For this reason, a good charger will draw down any remaining charge in a NiCad before recharging it. This adds a little more time to the recharging process, and uses a little extra power.

Fortunately, as the science of batteries advances, this becomes less problematic. NiMH batteries have improved to the point that we no longer buy NiCads at all.

NiMHs are less toxic, and can be disposed of more safely when they eventually wear out. They generally provide power for a longer period than comparable NiCads. Also, they are available in AAA size, our most commonly-used battery size. If NiCad AAAs exist, I’ve never seen them.

The main disadvantage of NiMHs has been their self discharge rate. A charged NiMH sitting unused in a drawer or appliance can drain after about 5 weeks. In recent years, NiMH technology advancements offer certain batteries in this format that hold their charge almost as well as NiCads.

We still have rechargeables of both kinds from when we first started using them in earnest, 15 or more years ago. This means we have a lot of batteries in our collection that lack the advantages of the newer generation batteries. We use these for less crucial applications, like LED candles, and focus on them in the winter, when we’re charge batteries more often. In the summer, when we use very few batteries, but need a flashlight or headlight to provide light dependably but unpredictably, we use the newer generation batteries in them.

Now that Aly lives “on grid” while attending college, we’ve been giving her our older rechargeables. She has more reliable access to power outlets, and can charge batteries more frequently than we can. Eventually, the “homestead’s” rechargeable battery collection will include only the more long-lived NiMHs.

Next time I’ll talk a bit about chargers, and recommend manufacturers we’ve grown to trust.

2 Responses to “Rechargeable Batteries (Part 3)”

  1. Survival Skvez says:

    Cadmium is a lot nastier than anything in an alkaline battery. I’d rather eat an alkaline battery than get NiCad leakage on my hands.

  2. Mark Zeiger says:

    Precisely so. Which is why we no longer buy them. Nevertheless, by using up the ones we have, we avoid all the additional alkaline waste that would otherwise be entered into the system.

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