FAQ: AA Batteries for Cameras
Posted by reedcat | Posted in FAQs | Posted on 09-03-2007
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The AA-size batteries are most comon power supply for digital cameras. Here you can found important issues about this batteries.
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Why AAs?
Thankfully, many digital cameras still take 4 (or sometimes 2) AA batteries of several different types. In decreasing order of utility, these include
- nickel-metal hydride (NiMH, rechargeable)
- lithium (non-rechargeable)
- nickel-cadmium (NiCd, rechargeable)
- alkaline (non-rechargeable)
And what about modern lithium ion (Li-Ion) batteries? Their electrically not compatible with the AA format.
My preference for AA-compatible cameras rests on these undeniable AA charms:
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Highly standardized.
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Cheap—at least compared to most proprietary alternatives.
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Compatible with a wide array of readily available chargers, which are also cheap thanks to competition in a large market.
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Available in a pinch wherever civilization is found.
Why not Alkaline?
Usual Alkaline batteries simply aren’t up to this task.
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an inherently high internal resistance
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electrolyte depletion in the reaction zone with slow recovery due to an unsophisticated but cheap to produce internal cell geometry that hampers remixing
- electrolyte dilution in the reaction zone due to the electrochemical production of water with slow recovery once again due to that cheap diffusion-limiting cell geometry.
On this case Alkalines can be used as spare power supply, when your rechargables are empty and you have no time or no socket for charging.
Why namely NiMH?
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Standard form factor (AA)
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Low cost—under $1.50 per AA
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High capacity (2000-2500 mAh per unit)
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Excellent high-drain performance—just what digital cameras demand
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Flat discharge curve—you can actually draw most of the rated capacity
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Light weight
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Carefree rechargeability—charge them whenever you like without fear of a NiCd-like “memory effect”
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Minimal maintenance—very occasional conditioning will bring you peak performance, but it’s by no means necessary
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Long lifetime (500-1,000 charges)
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Environmentally friendly, thanks to their reusability and lack of toxic heavy metals
What Pro&Contra have different types of AAs?
Just look on a table:
| Comparison: AA Batteries for Digital Cameras | ||||
| Feature | Nickel Metal Hydride (NiMH) | Nickel-Cadmium (NiCd) | Lithium | Alkaline |
| Nominal voltage | 1.25 | 1.25 | 1.5 | 1.5 |
| Rechargeable | Yes | Yes | No | No |
| Capacity per AA (mAh) | 2,000-2,700 | 1,100 for high-capacity types, 650 standard | ~2,700 | 2,500 |
| Cost per AA ($US/Euro) | 1.00-3.50 | 1.00-2.00 (high-capacity) | $2.25-2.50 | $0.25-1.00 |
| Cost per amp-hour | 0.50-0.80 | 0.80-1.8 | $0.83-0.93 | $0.10-0.40 |
| Cost per Ah for 1,000 uses* | 0.50-0.80 | 0.80-1.8 | $830-930 | $100-400* |
| Weight, approx. (gm) | 25 | 22 | 14 | 23 |
| Runtime in a digital camera | Very good | Good | Excellent | Very poor |
| High-drain performance | Excellent | Excellent—even better than NiMH | Excellent | Very poor |
| Self-discharge rate | 10% first 24 hours, then 10%/month | 50-67% that of NiMH | Negligible | Extremely low |
| Shelf life (once fully charged) | 3-5 weeks at least | Slightly better than NiMH | 10 years | 5 years |
| Voltage curve slope during discharge | Nearly flat over 1st 90% of capacity | Same as NiMH | Nearly flat | Strongly falling at start |
| Lifetime charging cycles | 500-1000 | More than NiMH | n/a | n/a |
| Maximum safe long-term trickle charge rate (mA) | 120 mA for normal charge, up to 1000 mA for express charge | 2-3% of rated capacity (C/33) | n/a | n/a |
| Operating temperature range | 0°..+50° Celsium | 0°..+50° Celsium, capacity suffers at low temps | -20°…+60° Celsium | Poor |
| Heavy metal toxicity | None | High, due to cadmium content | None | ?? |
* Since alkalines deliver digital camera runtimes hundreds of times shorter than the other battery types in the table above, multiply the cost for 1,000 uses by 100 to get feel for just how wasteful alkalines really are in digital cameras.
How to charge correctly?
Good quality NiMH AAs will deliver years of cost-effective service—conservatively 500-1,000 charges per battery—provided they’re properly used and maintained. Using the right charger makes it easy to do the right thing.
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Charge, deploy and condition loose rechargeable NiMH AAs in fixed sets, as if they were part of a battery pack.
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Avoid overcharging like the plague it is.
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Do whatever you can to avoid overheating during charging.
A smart charger that knows when to quit on its own is the key to success here. Deploy your charger in a cool, well ventilated area. If your charger has a cover, leave it open during charging if possible.
The easiest and cheapest of them are designed for old-fashioned charging “with stabilized current”. This method is safe, but takes time. How much? Try to divide capacity value on a cell to 100 and you get a value that is an approximate charge time – in hours… It means that modern cells need about a day for full recharging, which is totally impractical.
Most improved devices “with microprocessor” can make this job much faster – as in a couple of hours. But you will pay for that with a shorter lifetime – the cells’ not yours.
Overcharging and Overheating
NiMHs are very robust as rechargeables go, but overcharging is a sure way to ruin both runtimes and service life. Overcharging begets overheating, which cooks the battery chemistry in untoward and sometimes irreversible ways. Prevention remains the only surefire cure.
Normal batterie temperature by charging is up to +50-52° C. To the touch, that’s a little hotter than average hot tap water. On this reason place charger on a place with good air circulation.
When charging NiMH AAs get overly hot, assume something’s wrong:
- your sets have gotten mixed up,
- a battery in the set has gone bad,
- or perhaps the charger’s not so smart.
Warning: Never install overheated batteries in your camera while they’re still hot!
How to save battery capacity?
The strategy is simple: when power is in short supply, avoid the camera functions that consume the most, store and use your batteries at the proper temperatures, and take advantage of external power sources whenever you can.
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Avoid using the LCD monitor, whatever it takes. The LCD’s the single biggest power sink in your camera.
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Avoid running the zoom lens motor. Turning a zoom camera on and off forces the zoom lens to extend and retract with each power cycle.
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Avoid using the onboard flash.
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Use your camera and batteries near room temperature as best you can.
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Store charged spare batteries in the coolest place you can find at or above freezing, but be sure to bring cold batteries back up to room temperature before using them.
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Use an external card reader whenever possible.
- Use an AC adapter to power studio, surveillance or TV review sessions and any unavoidable serial cable transfers.
Safe transporting
Why talk about battery safety with 1.2V? The short answer is: current
| Warning: Shorted NiMH AAs can deliver currents as high as 7 amps! |
Luckily, it’s physically impossible to short 4 AAs amongst themselves when stored alone in an insulating container—even a loose-fitting one. The concern is what’s outside the container, and how easily it might come into contact with the battery terminals or metal case.
To avoid this trouble there are special battery wallets, as a rule from plastic or nylon.