Batteries are the lifeblood of all photographers. Even film photographers have fun with batteries, because our flashes and meters and whatnot all end up requiring power. And, even more than memory or film, batteries are one of the biggest items we're always frustrated by. My G7 and most digital SLRs are fairly nice, in that you can (and should) pull the battery from the camera after you are done shooting and stick it in the charger. But then I start dealing with batteries for my flash.
There is a right way to buy, work with, and use batteries, but there's a lot of misinformation out there that nobody wants to correct. I was reminded of this when I was shooting with my father-in-law who was getting maybe 20 shots out of a battery charge, so he was using alkaline batteries instead.
I've got... ehrm... four chargers and quite a few rechargeable batteries.
There are pretty much four times you really want to use disposable batteries:
Most of the rest of us use rechargeable batteries because we can't afford to buy batteries in bulk and don't live nearly as interesting of a life as to require maximum charge.
You can avoid a lot of trouble early on if you pick the right sort of gear. This often times depends on how you intend to use the device.
The name of the game in interchangeable batteries turns out to be AA batteries. They hold enough power and are small enough and any drug store just about anywhere in the US will have them. And tons of people offer good NiMH batteries and they end up competing with each other and any of them will fit. AAA and C and D and 9v batteries aren't as popular except for certain uses. Mostly, devices that take C, D, and 9v batteries have been redesigned to use some other sort of battery. So most cameras and flashes and other photo gear that don't have a custom Lithium-Ion battery pack takes AA batteries.
The problem with electronics that take an AA battery is that they have no way of knowing or controlling what you put in the device. Did the user just put in a fully charged Ni-MH battery that will put out 1.2 volts for a long long time or a partially discharged AA alkaline that's down to 1.2 volts from 1.5 volts? Custom packages let the manufacturer put in some electronics and keep track of how the battery's supposed to perform and make sure that it fits exactly and prevent you from fumbling around with batches of batteries. The problem is that a lot of the older ones are just stacks of C, D, AAA or AA batteries packaged up, so you get only marginal improvements over fumbling with the batteries.
There is another type of battery that's good enough to be an alternative to AA batteries.... Lithium-Ion batteries. They have some great properties coupled with annoying downfalls. They are a necessary evil. They fit a lot more power in a smaller package and they actually work better if you keep them topped off. The problem is that there's no standard size, shape, or electrical interface, so you might find yourself out of batteries with no way to charge them if you are on a 2 week trek through the wilderness. Canon and Nikon make vertical grips for some of their SLR cameras that accept them, whereas Olympus has an adapter for the harder-to-find 123 batteries. But if your camera doesn't take these batteries, you will have to look at solar chargers or a generator.
Custom batteries have a habit of disappearing from the market when it is no longer profitable. I tend to think that it depends on the type of battery. If it's only used in point-and-shoots, expect it to disappear from the market faster than if it works in pro-level cameras. Often times, a single battery type will be shared between a bunch of models, so you pretty much have until the last model is discontinued.
The downside here is that they will stop manufacturing the batteries and end up with a good amount stored to handle the declining demand. Especially with lithium ion batteries, if you have a battery that's been sitting in a warehouse for a few years, it's not going to last very long for you.
Much of this depends on you. If you only take a few shots and only use your camera intermittently, a packaged lithium-ion battery can be great. If you expend a whole bunch of battery packs per shoot, Lithium-ion is also handy. If you are somewhere in between or spend time away from power plugs, you might like an AA battery. For flashes, it's often unavoidable because they just don't make Lithium-ion battery flashes.
A lot of older photo gear takes a variety of less popular battery shapes, like "123" photo batteries or button cells or any number of other batteries. You have to be careful about these because if you are going to swap them out frequently, you may not be able to find them or might spend a lot of money on them. Or you may not even be able to get the battery anymore. There were flashes that were designed to take "123" batteries and you probably want to avoid them.
The coolest, sexiest way to make electronics is to build the battery into it and provide a docking station. Of course, then you have to disassemble the works when the battery dies or if you want to keep a few sets of batteries. So this isn't always a good thing.
The second coolest way is to provide a charger inside of the electronics. But remember, you are carrying around all of that added circuitry with your hardware. For a laptop, that's nothing. For a camera, that will make a slim camera not very slim. So I have a Canon G7 and my father-in-law has a Canon camcorder. They both take the same battery, but his charges when you plug the power brick into the camera, but mine charges in a separate charger.
And some cameras have crappy battery ergonomics. The G7 and G9 have a unified battery-and-memory-card slot and you will have to take it off the tripod if you want to swap batteries. This is something you might not think of while picking out a camera, but it will drive you batty later.
A perfect battery would put out power forever and never require charging or maintenance. A realistic perfect battery would suck up power quickly when you charge it, output power at a steady rate while you use it, be able to be recharged for eternity, and never blow up if abused.
All real batteries have issues that you need to be aware of. The exact issues depend on the formulation of the battery, but it helps if I define the terms involved.
Most batteries discharge themselves over time. This means that if you take a fully charged battery, put it on the shelf, and take a look at it later, it'll eventually lose most of the charge. You can measure this in what percentage of the charge it looses each month.
Real memory effect happens only on certain battery types in certain situations. Generally a specific type of NiMH battery only used in satellites and only if you are in orbit and charge it down to the exact same point.
What most folks call memory effect (because it's shorter than saying "Batteries that start to suck") is usually something else. The problem is that NiMH batteries are advertised as not suffering from the "Memory Effect" but they'll still do things that people like to call the "Memory Effect". This leads to very frustrated people and internet flamewars.
People usually call this "memory effect" even though it's not. What happens is that a NiMH battery will tend to put out between 1.2 and 1.0 volts for 90% of the discharge life. But maybe you've got crystals forming on the electrode and suddenly it'll put out 1.2 volts for 10% of the discharge life and then put out maybe 1.0 volts for the next 80%. So you put your battery in and discover that the battery light is blinking after a few pictures, curse about "memory effect" and toss out a perfectly good battery that's still 90% charged.
Things tend to return to a point of higher entropy. This includes your battery. All batteries will eventually fail. Some of them will just have slowly decreasing battery life and you discover that your laptop that had a 3 hour battery life now only lasts for an hour. I've seen some laptops where suddenly it just won't hold a charge at all.
All batteries, if you abuse them too much, will eventually stop storing power properly. Generally this comes from overheating them, overcharging them, or discharging them until the battery runs in reverse.. which causes hot chemical reactions inside of the battery and permanently damages it.
In extreme cases, the battery can explode and spew toxic chemicals all over the place.
Many battery packs are made up of a collection of different battery cells, otherwise they won't put out enough power. If you take apart a NiMH battery pack, often times you will see a bunch of little AA or AAA batteries soldered together. And even if you don't make them up into a battery pack, if you use the same set of batteries over and over again, you'll find that eventually the batteries will all have different levels of decay, voltage depression, and power storage capacity, and so it's like voltage depression but even worse, because if you try to drain the battery pack completely, you are probably going to fry at least one of the cells in the pack.
Avoid these for photography uses. They are handy for smoke detectors and that's just about it. They were "long life" and "heavy duty" compared to Zinc-Carbon batteries, but Alkaline batteries are much better.
These are the disposable batteries you get in the store. Some of these (the "Titanium" batteries) are designed better for the sorts of loads they get out of a digital camera because many digital cameras will suck a standard Alkaline battery dry astonishingly quickly. I usually keep some Alkaline batteries with me in case I'm having a bad battery day. But these will add up real fast if you use them primarily. On the other hand, for things like remote controls, the power usage is so low that a rechargeable battery will probably self-discharge before you run out of power in an Alkaline.
There was once rechargeable Alkaline batteries but nobody liked them that much.
Mercury cells were great. They put out exactly 1.35 volts and they did it for most of the battery's life, so you could save some circuitry. The problem, of course, is that they also contain mercury and the heavy metal risk does not outweigh the benefits of being a smidge cheaper. Especially given how inexpensive the circuitry to regulate voltage is now. So they are pretty hard to find and are pretty much illegal to make in most places.
Silver Oxide batteries are almost the same, except less toxic. The problem is they put out more voltage than a mercury battery. Zinc-Air batteries put out the same voltage, but they don't last very long because they react with air.
These batteries are the curse of older cameras. Too much hardware uses mercury cells and you often times need to recalibrate or modify the gear to use it with a different type of battery because they don't have any voltage regulation circuitry.
These were the first useful batteries that you could recharge. They are heavy, but if you need to put out a burst of quick power, they work quite well.
They like to be kept charged. Car batteries use liquid acid, but you can also add a gelling agent to the acid and seal them up so they don't leak battery acid if you hold them upside down.
You'd see this more in older stuff. As far as photo gear, you mostly see this type of battery in massive battery-powered studio strobes because they can handle the bursty nature of charging up a capacitor pack.
The first rechargeable batteries intended to replace standard sized batteries was the NiCad battery. They produce slightly lower voltages than standard alkaline batteries (1.2 volts instead of 1.5 volts) so older electronics will sometimes be unhappy with them. However, just about everything you'd want to work with them works just fine, you can get them everywhere, and they are sold in the same sizes as alkaline batteries.
Eventually, people got mad about all the Cadmium in the batteries, so NiMH batteries came along. They have slightly different properties, but unless you want certain specific battery properties, NiMH batteries are better and less toxic.
There used to be Ni-Cad and Ni-MH batteries in customized casings for electronics, but that's gone away and most of those are now Lithium-Ion.
The problem with these batteries is that they are quirky as hell. NiMH batteries specifically like to be charged almost-but-not-quite-to-empty. Except for the most recent NiMH batteries, they have a fairly high rate of self-discharge. They will suffer voltage depression if you don't treat them nicely. And most obnoxiously, most of the chargers for them are crap.
Now, there are very few factories actually making these batteries, but tons of people selling them. There are two properties involved in a NiMH battery.
First, there's the overall capacity. Often times, there's a certain amount of lie included in the capacity, so you may discover that your 4000 mAH cells are outperformed by an old 1600 mAH NiCad and that you only get 4000 mAH out of the battery when you use it under the exact circumstances that the manufacturer intended it to last longest at.
The second is the self-discharge rate. In the past few years, they had a great breakthrough in this area. They can ship the batteries fully charged so that you can just use them right away. And they take a long long time to actually discharge. This does generally come at the cost of decreased capacity, at least as far as what the number printed on the battery says. The actual effects of the decreased capacity is debatable. Some folks claim that they hold their voltage for longer, thus you will get more flashes out of them.
I tend to buy the low-self-discharge versions instead of the old style, simply because after switching to the low-self-discharge batteries and getting a good charger, I am very rarely caught without power in my batteries and haven't need the alkaline backup cells very often at all.
They make AA batteries that are Lithium, but they put out a lot more voltage, so it may fry your electronics unless you get one of the "voltage compatible" types.
In the days of film, "123" Lithium photo batteries were popular because you could get a useful amount of autofocus power and flash usage out of them. Nowadays, they aren't nearly as cool because people aren't content to take one or two shots anymore.
The nice part about these batteries is that they are very lightweight and hold more power in the same sized battery. They are also much more expensive and I suspect these are much more useful if somebody else is footing your bill.
These are great and awful, all at the same time.
See, they pack a lot of power in a small package, which means that you get a lot more use out of them before they run out of power.
But they also pack a lot of power in a small package, which means that they can explode and injure you or start a fire. And, just to make things even more fun, water just makes them burn more. There's been a number of cases where batteries have been recalled because of various contamination problems that cause them to explode during normal use. And if you short circuit them or abuse them, they might randomly decide to explode.
In a move that has the film photographers of the world snickering because they've been banned from the cargo hold for years, Lithium-Ion batteries are being clamped down upon by the FAA because there is a fairly real risk that one of them could bring down a plane if it short-circuited inside your baggage. Which, given that most of these batteries have the connectors on the same end, means that if you have your keys and a uncovered lithium-ion battery in your pocket, you could have a rocket in your pocket in short order.
They have a fairly fixed lifespan. No matter how frequently use them, after a few years, they will be dead. Also, there are no generic design batteries -- all of them are fairly custom. This means that your digital camera will be mostly useless a few years after they stop making that format of battery.
Apparently, the amount of self-discharge is next to nothing. Mostly a battery just loses power constantly over time.
The nice accidental feature is that, because they are so damn dangerous when you don't charge them right, most of them are "Smart" batteries with part of the charger integrated, so they don't have the problems that Ni-MH users have with figuring out which chargers don't suck. There are both manufacturer-made batteries and there are knock-off batteries people make that are compatible. The problem is, if the people making them goes too cheap, they'll cut corners and that will cause your battery to blow up. There are some documented cases here.
The problem is that there is also some markup that the manufacturer adds, so, in theory, a knock-off company could make just-as-safe, just-as-well-designed batteries that still cost less. My suspicion is that the real people who cut the most corners are the counterfeiters, not the people who go out and point out that they are making knock-off cells. But I have no data, just a vague observation. There are tons of knock-off cells sold every year. And there are a few cases pinned to the battery exploding that come up every year or two, but not a lot.
I got a Sunpak 622 Pro, which takes 4 C-size batteries. A modern NiMH AA battery is almost as powerful as an alkaline C cell. So they make adapters that will hold a AA battery and turn it into a C or a D.
But you can get C and D sized cells too, and they'll last even longer, but they are expensive because they are a much smaller market. So if you are building something, it's better to run two AA batteries in parallel than run one C battery. But older stuff is different.
I'm underimpressed with my adapters. They don't seem to fit very well, so I got some NiMH C cells for my 622 Pro. The C cells are nice, actually. See, it's very rare that I expend two fully charged sets of AA batteries and the C cell is around 2x the power of a AA.... so it ends up that I never run out of juice. Then I keep the AA adapters around for if I run out of juice on the single set of C batteries.
You should note that I researched the heck out of this. There are a lot of really old urban legends going around and many of them are totally untrue.
For example, when I was younger, all the kids would take the batteries out of their boom boxes and "sundial" them to get that last bit of juice.