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You can skip the terminology and head straight to what's important here.
Battery versus a cell: Most people use these words the same way. Battery engineers only use "battery" to refer to two or more individual cells connected together within one package. Thus your watch probably only has a single cell, your flashlight has a couple of cells, and your camcorder has a complex battery with several cells inside the black plastic package. No big deal.
Throw Away or Rechargeable: Engineers call throw-aways "primary," and rechargeables "secondary."
Power is expressed in Watts. Multiply current, measured in Amperes (Amps), by Volts to get power in Watts. Power is the ability to do work. If you imagine this as water in a hose, Volts is the water pressure and amps is how many gallons flow. How much you can spray off your driveway is thus the water pressure times how much water flows at that pressure. Volts, Amps and Watts are always capitalized since they are named after men who invented much of this: Alessandro Volta (Italian) who invented the first battery, James Watt (Scottish) who designed improvements to steam engines and mathematician André-Marie Ampère (French).
Energy is power over time, measured in Watt-seconds (Ws), also called a Joule, named after English physicist James Prescott Joule. A kiloWatt-hour is 1,000 x 60 x 60 or 3,600,000 joules. Flashes often measure their power in Ws, for instance, 50 Ws is normal for a shoe-mounted flash and 500 to 2,000 Ws is common for studio strobes.
Capacity is how much current is stored by a cell. Even throw-away cells have these ratings, although only engineers worry about it or look it up. These ratings are plastered all over rechargeables. It's usually measured in Ampere-Hours or milliAmpere-Hours. 1 Ah is the same as 1,000 mAh. A 1,000 mAh cell can deliver 1,000 mA for an hour, or 1 mA for 1,000 hours.
In reality cells are measured at about a 20 hour discharge rate. Cells have less capacity when more power is drawn, thus a 1,000 mAh cell would probably die after a half hour if delivering 1,000 mA. When capacity is measured it is measured to a stated cut-of voltage and at a stated rate. The same cell will have completely different capacities when measured at different rates and to different cutoff voltages. Therefore when you see these numbers on a package they are meaningless unless the rate and cutoff are specified, which usually they aren't. In addition to plain lying, this explains why you shouldn't bother to compare different brand's ratings to each other.
Avoid these. They are also called carbon zinc, zinc-manganese dioxide, Zn/MnO2, and LeClanché. These are the oldest, crummiest kind. Remember when flashlights only worked for a few minutes before they started to get dim? These were the batteries! They never could deliver much power for anything. You can still get these throughout the third world and in discount stores. I was amused at seeing a Duracell ad poking fun of the Eveready brand of these. It was unfair since Eveready makes both these crappy kind as well as batteries far more advanced. Anyway, ignore these batteries for everything except things with very low drains. Don't use them for a flash. They work great in things that run for a year like smoke detectors and clocks. They die after a couple of years in storage.
Capacity: Eveready Heavy Duty AA: 1,100 mAh.
These are the most popular today and work great. There are some premium versions, like Eveready's e2 Titanium, that work a little better in high-power applications like flashes and digital cameras. Personally I find they cost more than the benefit they offer compared to the regular alkaline batteries. Alkalines come in every size, from regular AA, C and D sizes as well as little button cells for watches and light meters. They last for years in storage. I have a healthy set in a flashlight that still works great even though the install by date passed five years ago.
Capacity, AA size: 2,700 to 3,135 mAh. Most AA Alkaline cells offer a capacity of 2,850 mAh. The expensive Energizer e2 alkaline offer 3,135 mAh and the cheapest cells offer 2,700 mAh, all pretty much alike at low drains. That's why Consumer Report's testing suggested to get whatever's cheapest. Note that "Titanium" is just marketing poof; these are not Lithium or titanium, they're just alkaline.
Because Duracell, Eveready Energizer and Rayovac offer to repair any damage caused by leaking batteries I only buy them, and never store brands. Even though the discount brands offer the same performance for a lot less money, when you eventually have one leak in your camera you'll be very, very glad that you weren't using store brand alkalines! I had a flash damaged once, and the battery company actually sent me a new one! One device damaged but saved by a warranty easily pays for the extra cost.
Here are the addresses, as of February 2004, where you can send any damaged equipment. Be sure to check that these are current:
Rayovac's warranty is here. (June, 2005)
Panasonic introduced these in 2005. I have not tried them yet. They sell for the same price as alkaline AA cells. They have a higher initial voltage, 1.7V, compared to ordinary alkalines which are 1.5V. Thus when new flashlights will burn brighter with Oxyride than with other cells. This also means that the bulbs will burn out faster, too.
David Pogue in the NY Times on April 7th, 2005 did the best article I've read on the Oxyrides. You may be able to read it here if you're signed up with the NY Times.
David found that for high-drain applications, specifically in a digital camera, that indeed they lasted for 844 shots compared to 566 for premium alkalines and 354 shots for regular alkalines. GREAT!!!, and at the same price as regular alkalines.
On the other hand David found that the Oxyrides lasted less long than alkalines for low drains. They lasted about as long as alkalines when discharged at a four hour rate. Oxyrides were worse than alkalines at lower drains like a 10 hour rate.
Thus from David's observations Oxyrides are fantastic for high drains like digital cameras and I would suggest them also for electronic flash, but a poor choice for clocks, pagers and radios and things that usually run a long time on a set. For these regular alkaline are still better.
Lithium (note that Lithium also comes as Lithium Ion rechargeables below)
These are expensive. They were developed for the US military because they offer double the power in the same size with half the weight. This is important when you have to carry a month's worth of batteries for your night vision system in your pack. Today these are the batteries that run your camera and cost $10.
Hint: Camera stores make a lot of money selling batteries. Look around online to get much better deals than retail. Lithium batteries have shelf lives of ten years or more, so stock up and don't worry. They come in various special sizes for cameras and also AA. You have no choice for the special camera sizes; they only come in Lithium. You have many choices in AA size, here are some tips.
Capacity: Energizer Lithium AA cells offer 3,000 mAh, the same as Alkaline.
Tip: Use the AA lithiums only for things that draw a lot of power, like a flash or a digital camera. They offer the same life as alkaline in things like clocks and pagers. They offer greater life only when you draw a lot of power as in a digital camera or flash. Otherwise they cost $10 for a set of four compared to 99 cents or less for alkaline. I have never found the lithium AAs for less than about $2 a cell, let me know if you do. Amazon has them for $2.50 each, a pretty good price, here.
Tip: I have not confirmed what the data sheets say personally, however if it ever got as cold as freezing here in California I'd point out that Lithiums are supposed to work better than alkalines at cold (sub-zero) temperatures.
Tip: AA Lithium can't deliver much instantaneous power as other technologies. Thus you get the slowest recycling times in flashes. The lithium cells are designed this way because otherwise the lithium chemistry is so potent it would tend to heat up and explode. You'll get faster flash recycling with rechargeables or even regular alkalines. You will get twice as many flashes with the lithium, just not as fast recycling. This is a minor point. If I had someone else paying for my batteries I'd use lithium AA for everything.
Idea: There is a rechargeable CR-V3 system I've seen circulating under various sub-prime brand names. You can get one here for $30 with the charger and spare batteries here for $20. I've seen claims of these replacing two AA cells in addition to the throw away CR-V3. These only have a capacity of about 1,300 mAh, less than half of a throw away CR-V3 (2,900 mAh) and less than Ni-MH rechargeable AAs (typically 2,300 mAh today). I also see claims of it outrunning Ni-MH, so try it yourself. I'm a cheapskate so I refuse to own anything that uses throw-away $15 batteries, so I have not tried this system. If I used these batteries I'd order one today since as soon as you use it a couple of times you're already ahead.
Mercury cells are no longer available in the USA. They were used in cameras from the 1960s and 1970s. Mercury cells had the advantage of constant voltage all the time, so they were ideal as references powering CdS cell light meters.
There's more here on them.
I have had my Luna Pro meter updated to run on ordinary S76 cells and it works great.
Lead Acid and Gel Cells
The first lead-acid batteries were used for telegraphy by Gaston Planté in 1859 and became available commercially in the 1880s. It's interesting to note how rechargeable batteries have always been involved with communication; your cell phone today runs on a Lithium Ion battery described below. A lead-acid battery starts your car. They are filled with liquid sulphuric acid and you don't want to spill them. Lead acid batteries are also available with gelled acid, called gel cells, which doesn't spill and can be used upside down. Gel cells are used in home alarm systems, backup power systems and your home computer's uninterruptible power supply (UPS) if you have one. Lead acid is not used in photography, except as heavy duty supplies for some lighting equipment.
Care and Use: Lead acid batteries prefer to be kept charged all the time. They can deliver very high power. That's why they are perfect for use in your car: they can deliver thousands of watts to start your car, and then are kept charged as you drive around. Deep cycling them is bad for them, and there are special kinds of lead acid batteries designed for this. Likewise, they are perfect for use in power backup systems where they are very happy being kept charged for years just waiting and can deliver enormous amounts of power instantly. Most television networks each have a room full of lead acid batteries that are always kept charged. If the power goes out these batteries can deliver enough power to run the entire network headquarters for 10 minutes or so if they have to if the Diesel generator doesn't start immediately. Other kinds of battery need exercise; lead acid doesn't.
Charging: Lead acid is very easy to charge. They are charged to a constant voltage through some form of current limiter.
Alkaline: Ray-o-Vac invented rechargeable alkalines in the 1990s. They never caught on.
These were the first popular rechargeables for modern electronics. They got popular in the 1960s. They still offer the most charge and recharge cycles of any technology. They also offer the lowest capacity so you'll be charging them much more often. Ni-Cds are unbeaten in their ability to provide dangerous amounts of current instantaneously if short circuited. Therefore they're popular in cordless soldering irons because they heat up instantly. Caution: if you short circuit them with a wire the wire will immediately glow and maybe even burn up. You easily can hurt yourself if you throw them in a pocket with keys or change. This of course is a good thing allowing fast flash recycle times and fast frame rates when used in camera motor drives.
Capacity, AA size: 650 to 1,000 mAh, not very much.
Care and Use: Mandatory: they should always be fully charged and then run all the way down before being charged again. This means for most field uses you need two sets so you have a fresh set with you for when the first set dies. If instead you just charge them up when you need them you eventually will get very little run time. This is called the memory effect. They learn how little you use them and then only provide that much capacity. They're like muscles: you have to use them to keep them strong. You have to baby Ni-Cds so I don't recommend them for anything. They also contain poisonous cadmium and must be disposed of properly. I don't even know where you can buy these today.
Charging: At slow overnight rates even the simplest circuitry has been used to charge Ni-Cds, since you don't have to worry about them overcharging at the slow rate. More advanced circuitry is required to charge them more quickly since the Ni-Cds could blow up at faster charge rates if the charger is not smart enough to cut off the current. Smart chargers today are very common and can charge these in several hours or less. As soon as all the charge is put back you stop charging, simple.
Nickel-Metal Hydride (Ni-MH)
These are the most popular rechargeables today in AA and other regular sizes. They replaced Ni-Cds in notebook computers in the late 1980s and became available in AA size in the 1990s. They offer twice the capacity of Ni-Cds and require less babying. Most chargers recharge them in a couple of hours. Otherwise they are very similar to Ni-Cd, although don't have quite the peak current ability of the Ni-Cds or offer quite as many charge/discharge cycles.
The electrical energy fed to a cell turns to chemical energy as it charges. When the cell is full the power no longer can turn to chemical energy and instead turns to heat. If the charger isn't smart enough to know when to turn off, which was the case in the 1970s, the charging current needed to be low enough not to damage the cell from overheating. This is why it took 15 hours to charge Ni-Cd cells back then, and why the crummiest chargers still take overnight.
The speed of any charging system today is limited its ability to know when to turn off. If you continue to jam a lot of power into a charged cell it will explode; whoops! Today most Ni-MH and Ni-Cd systems take a few hours. They measure when the cells are full based on voltage fluctuations (they look for a slight dip in voltage signaling a full Ni-MH cell ) and / or the temperature rise that signals the end of charge. The cells are supposed to get hot at the end of charging; that's one way the charger detects when to turn off.
Regular three hour chargers are smart, but since they usually don't monitor each individual cell they still have to be careful since all cells aren't charged at exactly the same time. The first cell to finish charging still has power jammed into it while the other three cells finish up. This limits what's safe.
Rayovac has a unique system that charges their special Ni-MH cells in 15 minutes. They use charging control not just in the charger, but also use chips in each individual cell. This way there is no danger of one cell exploding while the other cells are still charging. With Rayovac's chips in each cell the charger jams in current like there's no tomorrow and each cell shuts off exactly when it needs to. From what I hear these really work well!
Capacity in AA size: 1,350 to 2,500 mAh. Look out, many shifty brands lie about their capacity. 2,300 is pretty standard in 2004 and 1,350 was typical in 1999. My 1999 1450 mAh Sanyos still outperform newer off brands marked 2300 MAH! in big letters, so buy quality and not specs. Anything from battery pioneers GE/Sanyo and Panasonic ought to be great.
Care and Use: They still should be completely run down and then fully charged each time. They give the best service and life this way. Avoid using Ni-MH if you don't intend to run them all the way down each time. I always have two sets with me, so I can replace the set in use when it runs down completely. The advantage of Ni-MH over Ni-Cd is that if they lose capacity from memory issues you easily can rejuvenate them by running them through a full discharge-charge cycle a couple of times. They do have memory issues, which is why you see so many sold as "memory free." Baloney; the problem just goes away easily by fully cycling them. Unlike Ni-Cd, I've gotten great service from every Ni-MH system I've used by always fully cycling it. I've got many more years of service from an old cell phone that used these batteries than the phone service facility could believe, and the Ni-MH AAs I bought 5 years ago still work as well in my flashes and cameras as when I bought them.
Where to get them
I have one of these great systems here. It's great for travel with its small size, a folding built-in plug, needs no cord or external power adaptor and runs on any power worldwide from 100 - 240 V and 50 - 60 Hz. All you need to use it anywhere from Japan to Iraq are a few passive plug adaptors.
Some people, especially amateur radio operators who have been using these things in their walkie talkies for years, love the Maha systems like this one here.
I also have one of these LaCrosse chargers, the best to get for home since it also measures capacity, recycles and even can rejuvenate cells.
If size isn't important, today I'd first try the brilliant new Rayovac 15 minute system mentioned above. You can get the charger here and the cells here. I'm unsure if the charger includes cells or not and I'm also unsure just how many cells come with the cells ordered alone at those links. It's much more powerful to charge so quickly and therefore is big, heavy, has a fan in it and doesn't run worldwide.
Caveat: 5 years ago Ni-MH was an advanced technology, so the only manufacturers who made them, like Sanyo, made them well. Today all sorts of garbage is out there, and on top of that many makers make bogus claims about capacity (mAh). My 5 year old Sanyos, rated at 1,350 mAh, still give me more service than another brand I was given with "2,300 mAh!!" printed in huge letters. Next time I buy I'll get anything made by Sanyo (who also has made them for Kodak and GE) or Panasonic and possibly Sony. I'd pass on anything lacking the name of a real company on them.
Charging: Ni-MH chargers are usually smart chargers which measure voltage and temperature to stop charging as soon as the batteries are full. Thus they can charge batteries as quickly as an hour or less since there is no worry about overcharging at the fat rate due to the smart charger. As soon as all the charge is put back you stop charging, simple.
These are the newest and best rechargeables, since they offer the most power, the smallest size, the lowest weight and require no babying like the Ni-MH and Ni-Cd. They are also the most complex and expensive. They were introduced in laptop computers about 1994 and became common in camcorders and everywhere in the late 1990s. They removed many pounds from each laptop and doubled the run time almost overnight. We would have no iPods or tiny cell phones and microscopic digital cameras today without these. Today every camcorder or digital camera and laptop computer uses these. They only come in special sizes designed specifically for a given piece of equipment and typically cost $30 - 100 to replace.
Care and Use: Completely different from Ni-Cd and Ni-MH, lithiums prefer to be charged early and often. They don't like to be run all the way down. You will get only a few hundred cycles if you run them all the way down each time, and thousands if you charge them up while still mostly full. Lithium Ion's life tends to be measured by how much total energy comes in and out of the battery and not by cycles. Actually you can get more total energy from the battery by only partly using the battery's capacity. Thus I always charge every Lithium Ion battery every night when I've used it the day before, completely unlike the other technology cells. I've gotten great service out of every one I own; I charge my cell phone daily and I've been using it for years.
Chargers: They require very special chargers, unlike Ni-Cd and Ni-MH. Lithium is charged at a fast rate to replace the majority of the charge, and then trickle charged to replace the last 25% or so. Thus you may see charge state indicators which let you know when they are almost done, which happens very fast, and completely done, which takes much longer. Because special charging circuitry is required they are not offered in sizes to replace regular AA or other batteries, since people like me would goof once and blow them up in the wrong charger. Also they don't come in the special 1.5V versions invented by Eveready as a disposable cell, so today you can't get the rechargeable lithiums in AA size.
Brands: Li-Ion batteries require complex charging circuitry and sensors. There are many cheap counterfeit copies out there which skip some safety features. These phonies can and do explode! Because of this I would never buy any non-original brand rechargeable battery to replace any of the specialized batteries in my cameras and computers. Sometimes even legitimate suppliers get stuck with bad parts. See the Nikon recall for instance.
USE IN ELECTRONIC FLASH
Most applications have a clear winner for what sort of battery is best. Only in some applications, like AA size, do we have so many choices. Here are some comparisons for use in an electronic flash.
(data from Nikon SB600 instructions, typical for most flashes)
Thus I use Ni-MH. If you don't shoot as much use alkaline. If someone else is paying and you're going overseas by all means just pack a bunch of lithiums.
Ni-MH give shorter recycle times even though they have less mAh than alkaline because Ni-MH have much lower internal impedance. That means they can crank out a lot more amps intermittently than alkalines. Flash uses huge amounts of current for just a few seconds to recycle, thus the Ni-MH can belt it out faster than alkalines. Alkalines are not very happy having to spit out a lot of current all at once, which is what flash needs, unlike a radio. Alkalines don't recycle as fast, but will last for years sitting in an unused flash, while Ni-MH will go dead just sitting there after a couple of months.
All modern batteries are loaded with powerful, poisonous chemicals and metals.
Actually except for the old carbon-zinc, you ought to recycle every dead battery.
This is easy in the USA. As I recall Radio Shack takes all batteries for recycling, and with more Radio Shacks in the USA than McDonalds (no kidding) it's not hard to find them.
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