Thursday, 3 January 2013

Battery Tips

Batteries 12I recently ran an Introduction to Lighting workshop, and I included a brief section on batteries. Batteries seem to have replaced film as the most consumable item in photography, and I thought I should outline my approach to batteries for the workshop attendees. How to minimize battery expense and maximize battery performance are reoccurring questions and the answers can be used by anyone using batteries. Which is pretty much everyone.

I should clarify that the thing most people call a battery is not really a battery. Rather, it is a cell. By definition, a battery is two or more cells. So why do most people use the term battery? It is impossible to tell the difference between a battery or a cell just by looking at it. You have to read the label. For example, in the photo above, the left and the right devices are batteries, but the middle device is a cell. I suspect that this is confusing for most people, and since most people do not really care what it is called, they use the term battery for both cells and batteries. This is the terminology I will use in this post. Since most consumer applications for batteries use either AA or AAA size batteries, I will focus only on them in my discussion.

Primary, Single-use Batteries


Regular batteries, also called primary cells, come in three main flavours, zinc-carbon, alkaline, and lithium. This one is an alkaline battery from Energizer.

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Zinc batteries are usually the cheapest. Alkaline batteries are now very common and are pretty close in price to zinc batteries. Lithium batteries are the most expensive.

While these batteries are cheap and can be found in almost any store, zinc and alkaline batteries can lose between 8 and 20% of their charge every year while in storage! While you will want to buy fresh batteries, doing so is not that simple.

First, the date of manufacture codes on the packaging are not easy to decipher, so you may not be able to figure out how long they have been sitting around (and losing charge the whole time). To add insult to injury, stores typically put their old stock on sale, so while you may be thinking you are getting a great buy on batteries, you are probably not, because they may have already lost a lot of their charge.

Second, you cannot test the battery to see how old it is. Hooking a battery up to a battery tester or voltmeter will not tell you how fresh it is. As you can see in these discharge curves, you can have an old battery that is nearing full discharge and its voltage will measure pretty much the same as that of a fresh battery.

The big battery companies are constantly introducing new features to address this issue and some are putting a "Use By" date on their packages.

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This will give you some guide to the freshness of the batteries, but since it is left to the whim of the battery manufacturer to decide what the date should be, it is not really as good as knowing when the battery was made.

Lithium batteries are rated for storage between 10 and 15 years, so they do not have the same sort of problem. Lithium batteries greatly outperform the other two battery types, as you can see in this second set of discharge curves. These batteries also perform over a better temperature range (-40 to +60 degrees C), making them ideal for outdoor photography.

Photographers should note that the term lithium refers to a very wide variety of battery types. In the middle of this photo is a disposable, primary battery that has a completely different chemistry from the other two secondary (rechargeable) batteries, which are commonly called lithium-ion batteries.

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Lithium batteries have one major safety issue: they can sustain a very high level of current. While you might think this is exactly what you need, it is a fire and burn hazard if you short a battery. I once was shooting with a photographer who suddenly complained of a pain in her leg. She was using lithium batteries and had placed her spares in her pocket along with some loose change. The batteries shorted out through the metal in the coins, producing enough current to heat the coins hot enough to burn her!

As a rule, I recommend storing all batteries so that they cannot discharge accidentally. Do not store batteries in a pile like this.

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You can leave them in the packaging,

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Or you can use a proper battery storage container. These plastic containers are very cheap and are available at most electronics and handyman stores.

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I use mostly rechargeable batteries and I have a system for storing them that helps me sort the charged batteries from the uncharged ones. I mark the inside case cover with a '+' and a '-'. When my batteries are charged, I store them with the battery + terminal matching the case's + marking.

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When the batteries are used and need to be charged, I store them with the battery + terminal matching the case's - marking. This "upside down" storage is my flag that the batteries in the case need to be charged.

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Since I have broached the topic of rechargeables, I may as well jump in and cover them in more detail.


Secondary, Rechargeable Batteries


Rechargeable batteries, also called secondary cells, are more convenient, and can work out to be much cheaper than regular batteries if you are a heavy user.

Rechargeable AA batteries come in two flavours: Nickel-Cadmium, a.k.a. Ni-CAD (NiCD) and Nickel-metal-hydride (NiMH). NiCD is not as common as it once was, because Cadmium, which is very toxic, is not very good for the environment and there were performance issues with the batteries. Rechargeable alkaline batteries made a brief appearance a few years ago, but NiMH pretty much is the only game in town these days for rechargeable batteries.

NiMH batteries are sold by capacity, as measured in milliampere-hours, or mAh. The first battery here has a capacity of 2500 mAh, while the second one has a marginally larger capacity of 2650 mAh.

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Besides the obvious benefit of re-use, NiMH batteries can sustain very high levels of current, making them ideal in high-drain devices like camera flashes. Take a look at this discharge curve showing only NiMH batteries, and then go back and compare it to some of the others above it. You will see the NiMH curves are very flat. This means they can hold their voltage almost constant while delivering high current.

Unfortunately, NiMH rechargeable batteries have three issues counting against them.

The first issue is that their nominal voltage is only 1.2V and not 1.5V. This can be an issue in some gear, particularly older electronic games, but in many cases today it is not a problem.

The second issue is over-discharge. This can happen when one battery drains much faster than the others in a group. The good, fresher batteries will then drive current into the other, more drained battery and damage it.

This happens to me every now and then in my flashes. I put four freshly charged batteries into my flash, but one battery is a little weaker than the others. As I use the flash, the weak battery becomes much weaker than the others until my flash stops working. This can happen after only a few flashes. My flash, like
most current electronic devices, senses what is going on and shuts down to protect itself and the remaining batteries.

When this situation occurs, pull the batteries and check the voltage on each battery. If one battery is very low but the others are fine, you may have a damaged battery. Set it aside for recycling - don't dispose of it in the garbage!

For this reason, it is wise to keep your batteries in a group (you can write a number or a letter on the side of them) and regularly check to see if one battery is constantly lower than the others.

Some devices, like flashlights, are "dumb" and cannot detect when one battery is down, so over-discharge is much more likely to happen. If you are using NiMH batteries in a flashlight, or like device, you need to be very careful and keep an eye on how your individual batteries are doing.

The third issue with NiMH batteries is that they lose charge in storage much faster than even regular batteries. In fact, their storage loss can be up to 20% on the first day! This can cause a lot of problems in devices like a TV remote control. These types of electronics do not demand a lot from their batteries and the batteries end up self-discharging before you actually use up their charge in the device. And since these batteries can self-discharge so quickly, you will end up replacing the batteries more often than if you were using regular alkaline batteries. Using rechargeables might end up costing you more in this case!

I use regular NiMH batteries only in devices that are very demanding, like my camera flashes. Since I know when I am going to use my flashes well ahead of time, I can charge my batteries and have a fresh set ready to use when I need them.

A few years ago, Sanyo introduced "low self-discharge" (LSD) batteries called Eneloop. The LSD batteries hold their charge for up to a year, making them a go-to battery for almost any application. Other battery companies have hopped on the LSD bandwagon. In Canada and the UK, Duracell markets theirs as StayCharged. I hear that Varta also have an LSD line-up, although I haven't seen them yet.

Sanyo has continued to drive the technology forward and has introduced the Eneloop XX, which they claim will work in temperatures down as cold at -20 C. I have not tried them yet, but I am looking to get my hands on some.

So what is the downside to the LSD batteries? Well, they initially had a much lower capacity than the regular NiMH batteries. While regular NiMH batteries could store up to 2400 mAh (or even higher), the LSD-type NiMH batteries typically stored only 800 mAh. Today, the LSD technology has caught up and 2500 mAh batteries are on the market.

No discussion of rechargeable batteries would be complete without some mention of the chargers that are available. While the battery companies have designed very effective fast chargers for NiMH batteries, I still come down on the side that you should use a trickle charger when you can. While I have no test data to back this up, it seems to me that pushing all of that energy through in a short period of time, and generating all of that associated heat, must have an effect on the chemistry of the battery. However, I do also use rapid chargers, because there are times when I need a battery quickly and cannot wait several hours to get one.

This Maha unit is my main charger. It can individually charge each battery and it will do both trickle and rapid charging. The only drawback is its size, but then it can charge up to 8 batteries, so it needs to be large. Maha also provides their own brand of batteries.

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I also have a small, rapid charger which is very convenient for when I am travelling.

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No matter which type of charger you use, be sure to let the battery cool before you put it inside anything. Also remember to take batteries out of the device if you are not going to use it for a long time (like a month).

Battery technology is constantly changing and you should treat this post only as an introduction. There are many battery-centric webpages out there that can provide you with the latest information on what's new in the world of portable stored power!












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