When your camera takes AA batteries, then you need a stash of rechargable batteries, ready for use when the ones in the camera give out. (Owners of the Canon S1iS need a minimum of 4 spare AAs.) The only type of rechargeable you should be using are NiMH (Nickel-Metal Hydride) batteries. You can usually tell them apart from other rechargeables, because they are the most expensive! But they also last the longest between charges. The most powerful ones you can get now are rated at 2300mAh (milliAmpere-hour).
(In a pinch, NiCad [nickel cadmium] rechargeable batteries can be used, but NiMH batteries are about 50% more powerful than NiCads. NiMH have two additional advantages over NiCads: no memory effect [NiCads need to be drained before being fully recharged], and no cadmium, a toxic chemical,exposure to which can damage lungs and cause kidney disease. Lithium rechargables are usually not available to consumers, because they have a nasty habit of exploding if not charged correctly.)
The low-cost styles of Energizer NiMH rechargers are vert attractive price-wise, but should be avoided. (THey look like the photos at left.) They have a fundamental flaw: they fail to provide a trickle charge. Leave batteries in this charger for a week or two, and you'll be installing nearly-dead batteries in your camera.
Here's why: NiMH batteries lose their charge over time. Unlike other kinds of batteries, these otherwise-powerful batteries are effectively dead after a couple of weeks. The solution to to own a trickle charger.
A second flaw in the design of the Energizer charger is that it must be unplugged to be "reset." You cannot just take out charged batteries and insert others; you also have to pull the charger out of the electrical outlet, wait a few moments, and then plug it back in.
One I just purchased for my daughter and her new digital camera is Ray-O-Vac's new 15-minute charger. It is limited, however, to recharging their own own brand of batteries in that short time; other NiMH and NiCad batteries take the usual many hours.The charger has a miniature fan to dissapate heat.
How can these batteries charge in a mere 15 minutes? Ray-O-Vac inventetd a new technology that they call In-Cell Charge Control, which monitors the internal pressure of the battery -- pressure that builds up from the heat created by the charging process. I notice that the charger has a pair extra pins, which I think touch a black band on the IC3 batteries to sense the battery type: 15-minute capable or regular NiMHs.
A drawback is that this charger costs 3x as much as the Energizer; the advantage is that batteries are ready in 15 minutes, and then are trickle-charged thereafter. (I wonder Zellers is getting rid of this line, because the 2-battery charger is reduced to CDN$35.) Other drawbacks: The 4-battery charger (which I need for my Canon S1iS) needs an extra powersupply brick -- making the total unit very heavy for traveling. And it includes just 2 batteries. (I notice that the 30-minute Energizer charger also requires the separate power supply.) The packaging promises a "free" car adapter, but then you have to add US$4 for shipping.
NiMH is also short for:
* Bulgarian Academy of Sciences (BAS) National Institute of Meteorology and Hydrology (NIMH).
* National Institute of Mental Health
How can you tell if a batter charge has trickle-charge? Check the papers that came with the charger; they should mention trickle charging. If you no longer have them, then....
A day after the batteries are fully charged (usually indicated by the LED light turning off or changing color), touch the batteries. If they feel warmish, they are being trickle-charged; if cold, then they are not.
If your camera includes a charger, then it probably performs trickle charging.