The what, how and why of batteries

Last updated 00:00 11/09/2007

RICHARD PARKER/Dominion Post

SHOCKING: Using the wrong kinds of batteries can cost you money, and get you zapped.

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Our modern lives rely on batteries. Whether it's a laptop, iPod or mobile phone, you couldn't live without these funny little devices.

They may be pretty much everywhere, but most people still don't know much about them.

That's a shame, since a little bit of battery knowledge let's you make smart choices when you're buying, helping you save cash and get the most out of your gadgets.

HOW BATTERIES WORK
Batteries store electrical energy as energy in molecules and atoms.

Basically you have two solutions (one at the positive terminal and the other at the negative terminal) that are kept separate by the body of the battery.

When you switch your battery-powered device on, you complete a circuit and link the two solutions, allowing a chemical reaction to occur.

This produces electricity that travels from the negative to the positive terminals, powering your device on the way.

BATTERY TYPES

NiMH - Nickel metal hydride are the most popular type of rechargeables on the market today. They don't suffer from memory effect like NiCads and go longer between charges than rechargeable alkalines. They are, however, usually more expensive and lose more power when they just sit around in a drawer. Make sure you recharge them before they go completely flat too, otherwise you might not be able to resurrect them. Most NiMH batteries can be recharged about 500 times.

NiCad - Nickel cadmium batteries are rechargeables but have all but been replaced by NiMH because they're heavier and suffer from "memory effect". This effect shortens how long each charge lasts if you repeatedly recharge them before they've fully discharged. A bigger problem is overcharging them, which can completely ruin a battery. It usually has to be overcharged for more than a day to do this though.

Alkaline - When you go out to buy some AAs at the store, this is what you'll pick up. Alkaline are cheap and provide plenty of power. Some manufacturers have types specially made for high-drain devices like cameras, but these tend to be a bit dearer. Avoid rechargeable alkalines and pick NiMHs instead.

Lithium - Rechargable lithium batteries power many of today's gadgets, like laptops and cellphones. Because they pack so much power into such a tight space, they can run quite hot, too hot to sit on your lap. Some can run so hot that sometimes they can catch on fire, though this is very rare (but spectacular when it happens).

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Other types - Silver Oxide and Zinc Air batteries are "button-cells" that are used to power things like hearing aides and watches. Lead acid batteries are usually found in cars. Older types like Zinc Chloride and Carbon Zinc are to be avoided. Some are slighter safer (because they tend to leak less) but the battery life is terrible.

RECHARGEABLES VS DISPOSABLES
Disposal alkaline batteries are individually cheaper and tend to last longer than rechargeables before you need to change them, but a house run on rechargeable AAs will recoup the extra costs pretty quickly, especially if you have battery powered toys for the kids.

Rechargeables are, of course, much better for the environment.

They're even better if you use a solar-power charger to fill them up again.

The best set-up is to have a charger and rechargeables around the house, and buy disposables when you need batteries in a hurry.

One point to note, though, is that NiMH batteries put out 1.2 volts rather than alkaline's 1.5 volts.

This means some devices that take a few AAs may not be able to draw enough power from NiMH batteries.

If you're shopping for rechargeables, we recommend Sanyo's Eneloop NiMH batteries.

They cost a bit more, but they come pre-charged, keep most of their charge for more than a year, and can be recharged about 1000 times.

A charger and two AAs sell for $50. See this week's giveaway.

When you toss out disposable or rechargeable batteries, it's best to find a place that will dispose of them safely instead of chucking them in a landfill where they leach dangerous chemicals. Sony Style stores will accept most types for safe disposal.

- © Fairfax NZ News