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The Care and Feeding of AA Batteries for your Photo Gear.

A lot of photo gear requires AA batteries for power, whether it be the camera itself, a flash unit, remote control device, or a host of other accessories. The popularity of this power source warrants some discussion as to the different battery types,which ones are best, and how to care for them.

 

 
Caution.


Do not use AA Lithium Rechargeable batteries in place of standard AA batteries. The voltage of these batteries is 3.6V. Standard voltages for AA batteries is 1.5V.
 

 

 

Battery Types

One trip to a well-stocked department store will leave you scratching your head trying to determine which battery type is best. You will find the following common battery types in a store, supermarket, or on-line. Not all of these batteries are suitable for photography:

  • Carbon-Zinc: Thes are typically refered to as "flashlight" batteries, but they are not appropriate for photography use. They are actually the most expensive batteries you can buy - given the typical power you they provide. Often, they cannot provide enough power to even work in a camera, and worse, they are very prone to leakage. If you buy a set of new batteries and find they do not power your gear - you probably have Carbon-Zinc batteries. They are by far the cheapest to buy at the store - but the most expensive when you consider the low energy they provide. Avoid these batteries at all costs.
     
  • Zinc-Chloride: This is a cousin of the Carbon-Zinc battery and have the same warnings. They are often marked "Heavy Duty", "Super Heavy Duty" or similar. Again - avoid these batteries.
     
  • Alkaline (Alkaline Manganese Dioxide): While there are both rechargeable and non-rechargeable versions of the Alkaline chemistry, rechargeable Alkaline remain somewhat esoteric, and this discussion is limited to the ubitiquis non-rechargeable Alkaline (Alkaline Manganese Dioxide) battery. Alkaline batteries still offer a good choice in performance vs. cost and availability.
     
  • Lithium (Lithium Iron Disulfide): This discussion will be limited to non-rechargeable Lithium, which are found in AA cells. While rechargeable Lithium-ion batteries exist in the AA format, they are commonly found in battery packs due to their higher voltage, and will not be discussed further. The non-rechargeable Lithium (Lithium Iron Disulfide) have a higher initial cost (in comparison to Alkaline), but they offer high power and extremely long shelf life, and will outlast all of the other battery types discussed here. If you need to store batteries for emergency use, they are perhaps the best choice for this application.
     
  • Ni-Cad: Nickel-Cadmium batteries have been perhaps the rechargeable battery-of-choice in the AA size for decades, but have lost favor with the appearance of Ni-MH batteries. As a result Ni-Cads are all but obsolete. Ni-MH batteries outperform Ni-Cads in virtually all aspects save one - high discharge current. Unless you need high current capability of Ni-Cad batteries, these days there is no reason to buy Ni-Cad batteries.
     
  • Ni-MH: Nickel-Metal Hydride. Can have excellent capacity and long shelf life. Two types of this battery exist. Low Self Discharge (called LSD) typically have a bit lower capacity, but they can retain retaining 80% or more of their charge after one year of storage. Standard Ni-MH batteries do not have the long shelf-life as LSD versions, but typically discharge within a month or two in storage. However, the standard versions typically offer about 25% more capacity. Ni-MH is the current standard for rechargeable AA batteries for all but the highest current demands.

     


Figure 1. Battery comparison.

 

 AlkalineNi-MHNi-CadLithium
Voltage1.5V1.25V1.25v1.5V
Typical Capacity1000-1500mAH1900~2500mAH1000mAH3000mAH
RechargeabilityNone100~1000 cycles100-300 cyclesNone
Shelf Life5~10 yr2~5 yr (per charge)1~3 mo (per charge)10~20 yr
Cost per Battery$0.75$3.00$3.00 $1.75
Cost per Use$0.75< 1¢ $1.75

Figure 2. Typical AA battery characteristics (of various manufacturers)

In the chart above, "Typical Capacity" is weighted to the typical discharge characteristics of a digital camera. For example, Alkaline batteries have been advertised to have as much as 2400mAH, but in the high-discharge environment of a digital camera, capacities in the 1000~1500mAH range are typical.

 


Selecting the proper AA battery - a video.

 

Battery Terminology:

  • Primary Battery: A non-rechargeable battery.
     
  • Secondary Battery: A rechargeable battery.
     
  • Amp-Hour (AH): A the capacity of a battery is usually expressed as Amp-Hours, which is simply an algebraic equation: Amps x Hours. If a battery can deliver 1 Amp for 5 hours, it can be said it's AmpHour rating is 5 AH. Most AA cells are rated in milliamp Hours, or mAh. One mAH = 0.001Ah, or one-thousandth of an Amp Hour. 1,000mAH = 1AH.
     
  • Trickle Charge: A charge that is low enough that the battery can be overcharged without damage. Overcharge is the point where the battery becomes fully charged, yet the charge current is still applied. At that point, the battery is said to be in an overcharged condition. Chargers that are known as "quick" or "rapid" must be disconnected before the battery is fully charged and enters into an overcharge state, or battery damage can result.
     
  • Capacity (C): Expressed as a ratio, it is a method of normalizing charge and discharge currents. For example 1C = the battery's AmpHour rating. A trickle charge is normally considered 0.1C, or 10% of the battery's AmpHour rating. Therefore a 2,000mAH battery if trickle charged at 0.1C, would have a 200mA charge applied. And a 2,700mAh battery charged at 0.1C result in a 270mA charge.
     
  • Open Circuit and Closed Circuit Voltage: When a battery disconnected and is not under load (supplying power) it can said to be open circuit. For most batteries, the open circuit voltage is typically the battery's characteristic voltage. If the battery's voltage is used to determine remaining capacity, it must be done under load (closed circuit voltage). For instance, a Lithium battery might have an open circuit voltage of 1.75V, but when placed under load, the battery will indicate a lower voltage (1.5V or less - depending on the state of charge). Measuring a battery in open-circuit condition will often indicate the full voltage regardless of the actual remaining capacity.


Voodoo Charging

Incorrectly charging a battery is perhaps the main cause of poor performance and premature battery failure.

To better understand charging, I can offer an analogy that might make more sense. Think of charging as boiling a pot of water. In this scenario, the temperature of the water is the amount of charge in the battery, with the boiling point equivalent to full charge. And the amount of heat applied is the charging current.

As you apply heat to the water, it's temperature begins to raise, and when it gets to the boiling point, the "battery" is fully charged, and the water begins to boil. Assuming the pot is covered, if the heat source is low enough, evaporation of the water in the form of steam will not occur, and the bubbles will be dissipated back into the water. However, if the heat source is too high, the boiling rate continues to increase, and soon pressure will raise under the cover, and eventually steam will escape.

It should be noted that you can use a high heat to get the water to the boiling point (rapid charge), but then the heat must be reduced to maintain a state of equilibrium. This low heat source in a battery is known as a trickle charge.

In a rechargeable battery regardless of chemistry, the same thing occurs. You can rapid charge most batteries up to the point where they become fully charged. During this phase, a chemical change is occurring which returns molecules back into the battery plates that were released into the electrolyte. The particular molecules depend on the battery chemistry.

When the battery reaches full charge, no more chemical change is possible, and the electrolyte begins to gas (or boil as in the analogy). If the charge rate is low enough, the gas is dissipated back into the electrolyte and equilibrium is achieved. This is known as a trickle charge.

However, if the charge rate is too high, the battery will gas, it's internal temperature and pressure will raise, and eventually it will blow the safety vent typically located under the positive terminal. For most AA batteries, the vent is not re-sealable, and once opened, the electrolyte can leak out or dry out. At this point, the battery is ruined.

General Electric did make some re-sealable vent Ni-Cad batteries in the '80s, but this is a rare exception.

Slow Chargers: Also known as trickle chargers, overnight chargers, or 16 hour chargers, these chargers supply a low charge rate to the battery that will completely charge the battery over time, and when the battery goes into overcharge, the charge rate is low enough as to be safe. A battery can remain under charge in these chargers almost indefinitely. Ni-MH batteries are especially susceptible to overcharging, and can easily be damaged if the charge rate is too high when the battery is overcharged.


Safety vents.


Don't mix "battery kit" fast chargers and battery brands.


Figure 3. Charge Rates

Fast Chargers: Fast (or Rapid) chargers typically charge the battery in one, two, or four hours, and use a charge rate high enough that it will damage the battery should the charge remain applied when the battery goes into overcharge. For the most part, the cheaper versions of these chargers cannot fully charge a battery. Convenience is swapped for capacity.

The cheapest fast chargers use a simple timed charge. With these chargers, there is a safety margin built in, and high rate of charge is cut-off when the battery is perhaps 75% fully charged so as to prevent any chance of overcharging. Batteries to be charged with these chargers must be fully discharged. Recharging a partially discharged battery can result in overcharging at a high charge rate, which will likely damage the battery.

Smart chargers are also fast chargers, but with circuitry to detect voltage, temperature, or some combination of the two, to determine when the battery is nearing the full charge state. When this point is reached, the charging current is removed. As with their cheaper fast charger brethren, the battery is not quite fully charged. However, the best smart chargers will change to "trickle mode" and apply a low charge rate to the battery which will top it off allowing the battery to achieve full charge. Like a slow charger, this low charge can remain on the battery without damage.

Charger Brands: It is common practice to charge Brand A batteries in Brand B charger. Battery manufacturer chargers; those that come with batteries in a "battery kit" are the most likely to cause problems. Cross-branding batteries with chargers is not a very good idea, at least for some FAST chargers. As each manufacturer's batteries have specific formulations and capacities, the algorithms used for determining when a battery is fully charged may differ from brand to brand.

Charging batteries in the wrong charger can damage them. In fact, you will usually void the manufacturer's warranty by charging a battery in a different brand charger. This not because of liability issues, it is because the battery can be damaged.

Please note that this caution is primarily intended for the typical manufacturer-made charger supplied with batteries. Using a purpose-built Fast charger that is designed to charge batteries from any manufacturer are generally safe as they typically have advanced circuity to detect overcharge conditions.

A slow charger (even those that come with batteries) can generally be used to charge any brand battery as long as the charger and battery chemistry is the same (i.e. using a Ni-MH charger for Ni-MH batteries), as there are typically no voltage/temperature circuity requirements to determine when the battery goes into overcharge. Slow chargers typically provide a safe trickle current that is 0.1C (or less) to the battery.


Only charge Sanyo Eneloop batteries in this charger.


Maha PowerEx MH-C9000 Charger/Analyzer

Bank Chargers: Found in some "battery kit" chargers, these inexpensive chargers electrically connect adjacent battery slots together, so that you have to recharge two batteries at a time - another good reason to avoid using different brand batteries in these chargers. Avoid combining different battery types and chemistries in these chargers. For example, you should never charge a AA and AAA battery at the same time in these chargers. Their capacities differ significantly, and the AAA battery will go into overcharge long before the AA battery will.

This restriction should even include avoiding charging batteries of the same size and type, but different capacities. For example, do not charge a 2,700mAH PowerEx battery in the same bank as a Sanyo 1,950mAH battery.

Higher-priced (non-banking) chargers usually allow battery types and sizes to be mixed. But always read the manufacturer manual to be sure.

Charger/Analyzers: A special breed of high end chargers, called Charger/Analyzers, such as the PowerEx/Maha C-9000 do an excellent job of properly charging Ni-MH and Ni-Cad batteries from any manufacturer. This charger typically employs sophisticated algorithms to measure voltage and temperature of the battery to determine when the charge current should be reduced or removed.

Recharging Non-Rechargeable Batteries: Some products exist on the marketplace that allow you to recharge non-rechargeable Alkaline batteries. These devices are sometimes called "battery-rejuvenators", "battery-recyclers" and the like. I don't use them. While they are said to be able to recharge an Alkaline battery up to 100 times, their effectiveness is debatable. My take on these devices are that you can sometimes purchase a set of 4 Ni-MH AA batteries and charger for about the same price these devices cost - so why not just buy rechargeable Ni-MH batteries?

Never, never, never, never put a non-rechargeable Alkaline battery into a fast charger. The best chargers will not allow you to start a charge cycle, but dumber fast chargers may. An Alkaline battery is especially not designed to be fast charged, and there may not be a safety vent. If this battery were allowed to be fast charged, it's internal temperature and pressure could raise to the point of bursting the cell and spewing electrolyte. It's not safe.

 

Charging Do's and Don'ts:
  • Don't recharge non-rechargeable batteries.
  • Don't cross-brand "battery kit" fast chargers and batteries unless you know for sure it's safe.
  • For maximum capacity, always trickle charge, or top off a fast charge with a trickle charge.
  • Never recharge damaged batteries (electrolyte spewing out, obvious signs of damage, etc).
  • Always discharge a battery completely before recharging it.
  • Always Break-in, or Condition your new batteries if your charger has the capability.
  • Only charge battery chemistries the charger was designed to charge.
  • Never mix rechargeable battery types, sizes, or capacities in a charger, unless it's safe to do so.
  • Always read, understand, and follow the charger manufacturer's instructions, capabilities, and limitations.