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Battery Care (Part I)


I tend to go like a runaway train the moment anyone asks me something like "What's the difference between rechargable batteries and the normal ones?" or "Why is that green one (the GP heavy duty version) cheaper than the gold one? (the GP alkaline version)"

There are alot more to batteries than what most people would think. In order to get the maximum out of your batteries, save some money on your batteries, or most importantly use your rechargable batteries more effectively and let them last longer (more cycles as well), you'd have to excercise good battery care. And that includes knowing your batteries well.

The average person probably comes across about 5 different types of batteries in their daily life, and I'm not even referring to sizes. The 5 types are, in order from most common to least common: Lithium-Cobalt, Alkaline, Carbon-Zinc, Lead-Acid, and Nickel Metal Hydride (NiMH).

The Lithium-Cobalt battery, more commonly known as Lithium Ion (Li-ion), is what is used in most proprietary batteries (commonly the square types) in mobile electrical applicances like mobile phones, mp3 players, PDAs, laptops, cameras, etc. They are the most energy dense, meaning that they deliver they contain the most amount of charge per unit volume, and also the most expensive. The chemical make-up of these makes each battery cell output 3.7V typically. They can be charged quite fast, and have absolutely no memory effect*. Lithium batteries are unfortunately the most dangerous type of battery. That is not to say that they are not safe if used properly though. These types of batteries cannot be charged over 4.2V or discharged under 3V. Most proprietary batteries have a built in circuit to regulate charging and will cut off the power automatically if the battery reaches 4.2V (full charge) or stop the battery from discharging any further once it goes under 3V (empty). However, when storing such batteries on the shelf as spare, it is very possible for the voltage to drop below 3V. Some internal protection circuits sensing this will prevent charging of the battery when this happens. That is because, outside the operational range of the battery, there may be some chemical changes in the cell that would cause the battery to act differently when being used or being charged. This could easily result in venting, which the battery might pop, explode, or a part might tear releasing very hot fumes (that can scald or burn you). In the light of this, it is always wise to check the battery voltage for such batteries when returning them to use after having sat on a shelf for a significant period of time (above 1 month). Some batteries, like those found in laptops, have more than 1 cell inside (it will be stated on the battery itself), and so you must account for that when checking the battery voltage. Remember each cell has a operating range of 3V-4.2V. So for example, if the battery has 2 cells, the voltage range should be 6V-8.4V. 3 cells, 9V-12.1V. You get the idea.

Alkaline batteries usually have the word "Alkaline" stated on the battery itself. These batteries are great for high consumption devices like torches and toys. They work fine for digital cameras that use AA batteries, but NiMH batteries are a better alternative. The chemical nature of an alkaline battery allows it to produce a high current when needed and are also quite energy dense in comparison to the zinc-carbon counterparts.

Zinc-Carbon batteries usually are labelled something along the lines of "heavy duty". Contrary to the labelling, these batteries are very bad at high current uses. You'll get what I mean if you put any of these in a digital camera or in a toy car and compare it to the performance of its alkaline counterpart. Most torches still work fine with these, but not for as long since the capacity of a zinc-carbon battery is quite inferior to an alkaline one. However, the plus point of these batteries are that they are cheap, and significantly lighter. About 20% lighter in terms of weight, and depending on what brands you buy, around 50% of the price of alkaline batteries. These batteries would be perfect for running low consumption appliances like clocks and weighing machines since these don't require the juice that an alkaline battery provides, and you can reduce your cost.

I just put lead-acid batteries in there for the fun of it. It's true most people will encounter it (it's a typical car battery!) but it requires only the occasional maintainence of topping up distilled water. There's not much you can do anyway by yourself since the acid and plates need replacing once in a while which can only be done cost effectively by professionals. However, it's still a battery that you will encounter, so you might as well know a bit about it. Lead-acid batteries are probably the only liquid type battery still being commonly used. It is the worst in energy density and is very troublesome to bring around. Despite this, these batteries are still used because they are very easy to maintain day to day, and are capable of providing extremely high currents in bursts. (To start a car, up to 100A has to be drawn from the battery for a few seconds!) Like lithium batteries, the voltage of lead-acid batteries must be maintained within a certain range of around 11.1V-13.4V. Reasons are similar to the lithium batteries, but there's no risk of explosion (unless you're dealing with a sealed lead-acid battery which most of you won't know about anyway). The car charger automatically helps you maintain that range, and you very rarely leave your car untouched for months at a go anyway.

Lastly, Nickel Metal Hydride (NiMH) batteries are the most common rechargable batteries that exist as AA, AAA, D, or C size. They are one of the best at putting out high currents continuously and they are also about as energy dense (depending on the capacity you buy) as the alkaline non-rechargable counterparts. They can be charged very quickly (around half and hour to an hour) too. The set-back is that these have a high self-discharge rate and a small amount of memory effect*. Memory effect is not to be worried about too much as it's rarely possible to discharge the battery to the exact same level each time before charging. Self-discharge is, however, a major problem. All batteries discharge by themselves slowly. That is why it's always advisable to measure the voltage of each battery before use if it has been on the shelf for a long time. Primary batteries (batteries that cannot be recharged) have very low discharge rates. Something along the lines of 10% per year. NiMH batteries discharge at around 40% per year when new, and faster as they get older. This makes rechargable batteries only viable if they are to be used frequently, or for short periods of time intensively, like in a camera while on holiday, in an electric toothbrush, a shaver, or in toys. NiMH batteries have an operational voltage too. This is anywhere from about 0.8V-1.3V. Going above or below this range weakens the performance of the battery and might cause it to leak. Not much danger though as there are no explosions, venting, or popping.

*Memory effect comes about when a rechargable battery is charged repeatedly after being only partially discharged (used) to the same level consistently, and thus reduces the capacity of the battery. The battery "remembers" at what level it was previously discharged to and thus fails to output anymore power when reaching that same level again hence giving the impression that the battery is out of charge (flat).

15:24 29 Aug 2010
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