Rechargeable batteries have been frequently described as frugal and environmentally friendly. And to a certain extent they are. But to get the most bang for your buck and actually minimize your environmental impact, you have to know which type of battery is best for different situations.
Batteries release electricity when a chemical reaction inside the battery occurs. Your basic alkaline batteries are single use, the zinc/manganese oxide/potassium hydroxide reaction is not reversible. In rechargeable batteries, running electricity through it reverses the reaction – hence recharging it. There are several different types available. In the past, rechargeable batteries were dominated by NiCad (nickel cadmium), but are now being succeeded by NiMH (nickel metal hydride), its less toxic cousin. Lithium batteries are mainly used in high energy demanding products, such as laptops and cell phones.
When accessing batteries, there are several factors to consider. Self-discharge rate refers to how quickly a battery losses charge while not in use. Nickel batteries loose charge very quickly, although the low discharge NiMH are better, while lithium and alkaline hold it very well. Capacity describes how much energy a battery hold and can release over time. The low discharge NiMH have a smaller capacity compared to regular NiMH. The number of times a battery can be recharged also varies between types. Rechargeable alkaline can be recharged the least, and loose potential capacity with use. (Other rechargeable batteries will fall off with so many charges, although many NiMH are advertised to last 1000 charge cycles.)
Single use alkaline batteries can hold most of their charge for years. Which is why the expiration date on those packages is often several years in the future. Unfortunately, even the low discharge NiMH are no where near as good at holding charge over years. So for safety items, such as emergency flashlights or smoke detectors, you will want to use disposable alkaline. The last thing you need in an emergency is a bunch of dead batteries.
Rechargeable batteries cost 5-15 times more than non-rechargeable. They also require a good charger – cheap charging devices can overheat the batteries, causing them to wear out sooner. Assume an investment of about $20 for four AA batteries plus charger. Thus to break even, you will have to replace $20 worth of regular alkaline batteries over time. (The energy costs of recharging are negligible for these calculations – only pennies.) Additional sets of four will only cost you an extra $7-10, reducing your break even point. Also keep in mind you will need an extra 2-4 batteries sitting around full charged for when you need to change some out.
Some items, like clocks or a TV remote (assuming you are not a 24/7 channel surfer), have very low but long term energy needs. With the high self-discharge rate of NiMH, it is impossible to break even before the rechargeable dies (several years) and it is much more of a hassle. Also, certain devices require a starting voltage of 1.5v, which regular AA alkalines can provide but NiMH AA (1.2v) cannot.
Other devices, such as my cordless mouse and mp3 player are much better candidates for savings with NiMH. My mouse would go through about four regular batteries a year, so within 2 years I come out significantly ahead. I find they work decently in a pinch for my digital camera, but disposable lithium batteries last much longer. (I have had better luck with Energizer brand than Duracell.) The more devices you have that go through batteries regularly and do not sit unused for weeks at a time, the greater your potential savings from rechargeable batteries.
For additional perspectives, check out this savings evaluation for four common devices and this article looking at why rechargeable batteries rarely are cost effective.
Battery toxicity is an important consideration, but pollution caused by the production and distribution should also be considered. Rechargeable batteries can significantly reduce all of these. Unfortunately, the only major study of the environmental impact of rechargeable vs. disposable batteries was done by Uniross – a manufacturer of rechargeable batteries. They found that rechargeable batteries have “up to 32 times less impact on the environment than disposable batteries.” Of course, minimizing environmental impact depends on choosing the right type for each device.
Proper disposal of any type of battery is essential. If you do not know where you can drop them off for safe recycling, check out Call2Recycle and use the “Drop Off Locator” based on zip code. Also, look over their tips on maximizing the life of your rechareables.