Rechargeable batteries are being increasingly used by digital cameras. However, many people remain unaware of how to best maximize the charge lifetime of their batteries. This article presents a general overview of care, as well as specific tips for different types of batteries.
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Tips on General Care
Most importantly: Be nice to your battery! Don't do anything to it that you wouldn't want done to you. Don't drop or shake the batteries, and don't expose them to extreme temperatures. If you're carrying replacement batteries with you, then store them deep in your bag as opposed to the outside compartments, so that they won't be as exposed to jostling and temperature changes.
When not in use, keep your rechargeable batteries in a cool, dry place. However, try not to leave batteries in storage for long periods of time. If possible, use them at least once every 2-3 weeks.
If the contacts on the batteries are dirty, gently clean them with a cleaning solution (which you can make yourself) and a cotton swab. This will allow the most efficient discharge of power from the battery to the camera as possible.
All rechargeable batteries, no matter how new or expensive, have a limited number of possible charges, and the duration of those charges inevitably decrease over time. Thus, the fewer times you have to charge them, the longer the batteries will last. Practice good power-saving techniques. On your digital camera, run the LCD brightness at the lowest light level you can, and try not to leave the camera on for extended periods of time.
When you first purchase new rechargeable batteries, they (should) arrive in a discharged state, which means you'll need to charge them first thing. Furthermore, they won't reach their maximum capacity until they're charged and discharged several times. Some people will thus "tone" their batteries by charging and discharging them a few times before actually using them out in the field.
Also, make sure both the charger and the camera are calibrated to the discharge pattern of the particular battery - for batteries and battery charges purchased from the same camera company, this shouldn't be an issue, use of off-brands and DIY projects does not have this same guarantee.
When the lifetime of your rechargeable batteries is done, don't forget to recycle! All rechargeable batteries contain compounds toxic to the environment, and so need to be taken care of in special facilities.
Care also differs slightly depending on the type of rechargeable battery you use:
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These are probably the most common battery used for cameras, being both stable and fairly high-capacity, and don't lose their charge excessively between uses. However, they suffer from the “memory" problem—that is, if you don't entirely drain the battery between charges, it won't charge as much the next time. Thus, Ni-CAD batteries work for shorter and shorter periods of time. Typically, they require replacement every 1-2 years.
If using Ni-CAD batteries, make sure to drain the battery entirely before charging it. For a photographer, the best way to alleviate this is to keep a spare battery on hand, so that as soon as one is entirely drained the next can be used without having to stop and recharge. This is known as a “deep discharge", or “conditioning". If you don't keep replacement batteries on hand and so can't practically run the battery all the way down while out in the field, try to at least do one deep discharge a month.
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Ni-MH batteries are a newer technology that manages to encompass many of the advantages of Ni-CAD batteries without suffering the memory effect. They typically last 3-4 years without replacement, and hold longer charges.
However, they have a different drawback: when not in use, they have a high discharge rate, typically losing 20% of its charge per week. To prevent this, it is recommended that when not in use Ni-MH batteries are kept within the charger.
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These are the newest battery on the shelf. They have all the advantages of the previous two generations of rechargeable batteries, plus a longer lifetime. They tend to last 4-5 years, about 300-500 discharge cycles. However, they lose about 10% of their total capacity each year due to general deterioration.
To maximise their lifetime, it's best to keep them in the charger when not in use. Using the same “deep discharge" technique as with Ni-CAD batteries will also extend the battery lifetime.
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For a closer look at the difference between Ni-MH and Li-Ion rechargeable batteries and suggestions of which type you should use and where to buy them, please read this article on green batteries.