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Revised  October 13, 2002
Revised  December 5, 2006
Page 3 Revised

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Nickel Metal Hydride

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Why Batteries

This article originated after I had bought a camera that uses 4 AA to power it up. I tried Alkaline batteries, just because I had been using them for a walkman and they had lasted a long time there. But not so in my new Olympus C4040 camera, which the sales person warned me about during the purchase. I knew about rechargeable nickel - cadmium batteries because I have been using them for over five years in things like: flashlights, a walkman, and other battery powered units.

I had never used a nickel metal hydride battery and had no idea other than it was rechargeable and that they held no memory like the other batteries I had used. I figured that I would go to the closes Radio Shack since I had a discount card that would save me 20 percent off their regular price of batteries. I also figured that if anyone knew about batteries they would.

During my visit there, I was greeted by a young lady who knew nothing about batteries, but tried to get answers from another sales person. The other person was so ignorant in the way that he answered her, that my first thought was to walk out. However it was not her fault, she was new to this store and this sales guy must have been in the wrong profession. I bought the batteries and a charger not knowing anything about them except that they did not hold a memories.

However I learned quickly that they are a whole lot different than any other battery I have ever used. If you don't use them properly you will either  have a fire or have a short lived battery, -- which other wise are remarkable to use. So I felt it important to learn about them and than pass this information along to you, so that if you need a rechargeable work horse battery that you will know how to look after  them.

Rules of Life

Note to readers : This article is only to inform you so when you do buy batteries that you will have enough knowledge to decide if these Nickel Metal Hydride Battery will fit your needs or not. Also I am by no means putting Radio Shack down, they are an excellent store and at most times their staff can be relied upon for good knowledge and accurate information.

The Olympus C - 4040 zoom camera came with 2 lithium 3 volt CR - V3 non - rechargeable batteries. I thought that I would use alkaline batteries first and I am glad I did. Lithium batteries work very well in cold weather but are costly to buy and so they should be used as a back up to Nickel Metal Hydride Battery or Ni - MH the shorter name for them.

NiMH are cost - effective and can offer between 500 to 1,000 charge charges per battery - provided they are properly looked after. A few important practices to learn and your on your way.

A few Golden Rules:

Rule 1. These batteries do not like to be overcharged.
Rule 2. Excessive heat during charging will destroy them or cause a fire.

Rule 3. Always charge NiMH in fixed sets, as if they were part of a battery pack. Never mix batteries between other packs.

Rule 4. Look for a smart charger that has a built in timer and knows when to shut off. Use the charger in a cool, well ventilated area like a basement. Keep the cover of the charger open, during charging to vent off the heat created from normal charging.

Remember these few rules and these NiMH batteries, will last for many years.

What is a Nickel Metal Hydride Battery ?

 Nickel-metal hydride (NiMH), batteries of course. Can be used in place of all existing types use now, AA are common among camera users, however there are other sizes available : AAA, 9 volt, D and C cells too.

  • Thet can be used like any (AA) battery with a life expectancy of twice that of an alkaline battery.
  • Are cost efficient because they are rechargeable and last longer than other rechargeable on a single charge.
  • They have a high capacity of 1300 to 1800 mAh per AA battery cell.
  • They perform excellent in high drain digital cameras which have LCD monitors and flashes.
  • Flat discharge curve- you can actually draw most of the rated capacity.
  • They are made of different materials that make them light weight.
  • They can be recharged at any time or whenever you like without the fear of a NiCd - like memory effect.
  • They need minimal maintenance: a good charger can successfully condition them back to maintain peak performance.
  • They have a long life of 500 to 1,000 charges per each AA battery cell.
  • The best of all is that they are environmentally friendly, thanks to their reusability and lack of toxic heavy metals.

How Long will they Last?

Any rechargeable batteries will lose its' charge over time even when not in use. NiMH batteries do so even faster than lithium rechargeable (if you can afford them to buy) (Lithium rechargeable are most often found used with Camcorders). A satisfactory run times of one AA set is from 3 to 5 weeks. So it is a good idea to carry an extra set or two just in case the batteries your using go dead.

NiMH batteries that are removed from the charger when fully charged, will lose about 10 percent of their capacity in the first 24 hours and 1 to 2 percent daily at room temperature. If batteries are stored in warm temperatures this will increase discharging, while cooler temperatures will slow discharging down. At about 1.5 percent per day after the 1st day, that leaves a residual charge of 58 percent at the end of the first month. If you're coming down from, say, 1600 mAh, the remaining 928 mAh per AA will still power quite a few shots.

Battery Memory

 No memory what so ever .

No worries about recharging your NiMH AAs before they die in your camera or palm computer. Avoid overcharging your batteries, and you will never see a memory effect like we all have came to know and hate in NiCds batteries.

Charge your NiMH AAs whenever it's convenient but less is still better. Waiting till they are at the end of their power cycle is not necessary with these batteries.

Why Keep Batteries in Sets

I never had to keep any other battery before these ones in sets. However with NiMH it is important to keep them in sets. Depending on what they are used for in my case it was a camera that uses four AA battery cells and an extra four batteries as a spare. It is important to keep those four batteries in the camera together. So I labeled the first four bateries as set One. Each battery had on it set one battery "A", set one battery"B" ect. The back up set I labeled as set two, battery "A" , set two battery"B" ect. Why bother keeping sets of batteries together? Here's why:

Charging multiple batteries in different states of discharge can easily damage the batteries, and the charger.

Here is what you need to do: put together in dedicated groups of 2 batteries or 4 batteries of complete sets. A complete set means that the batteries all started out together as brand new. Mark each battery as in a set of four like this: Set1 battery1, Set1 battery2, Set1 battery3, Set1 battery4 and the second set is marked like this: Set2 battery1, Set2 battery2, Set2 battery3, Set2 battery4. Mark all additional sets the same so that you can not easily mix them up when using or charging.

It is important not to mix these battery set because you want them to discharge over time equally. So never, ever break your sets up. When you need to replace batteries in a set, try to get the new and the old batteries in sync separately as best you can before charging
them together. It is better to replace the group of batteries than to add a new battery cell to the older group.

A Good Charger

A good charger will do most of the work for you and help your batteries last through many charging cycles. Most will charge Nickel - Cadmium as well, but never charge the two of them together. Charge one or the other in the charger at one time only. For better comparability I suggest that you uses the same manufacture for both your batteries and charger.

A smart charger will be able to conditioning and charger your battery with in a short period. I picked up a charger from Radio Shack that will charge eight "AA" cells in under two hours. It uses a pulse conditioning charge which is suppose to lessen the chance of causing harmful gas bubbles. The charger has an indicating light which tells you that you are in the charge mode or that the battery is dead. The charger allows you through a switch to charge batteries in sets of 2, 4, 6 or 8 at one time. It has a timed charge and will never over charge. It also has a short- circuit protection and senses batteries that have been place in the charger backwards and in a reverse polarity.

Points of a good charger are:

  • It uses a microprocessor  to sense temperature and charging cycle.
  • It will fully charge 4 AAs from dead to full charge in about 2 to 3 hours.
  • It will not overcharge
  • It will condition your AAs.
  • It is small and light weight to transport and store.

What Should you look for in a Charger

 Look for a charger and batteries from battery manufactures rather than the one offered by the camera manufactures. These usually cost much more however, Kodak chargers and batteries seem to be an exception. I recommend going with the Universal Battery Charger catalog number 23 - 422 from Radio Shack.

Fast Chargers

Buy a fast charger for your NiMH AAs, and an extra set to have on hand. Look for one that will monitoring the batteries temperature so that you batteries are not harmed.

Shop around for a NiMH chargers,

  • Fast (500 mA) NiMH/NiCd
  • Some will charge AAA/AA and 9 volt charger,
  • Radio Shack AA battery cell rated at 1600 mAh
  • 110-120V AC adapter
  • A 12V cigarette lighter charger is good for those long holiday trips. The car adapter is used.
  • The is a built- in conditioning circuit activated when needed.
  • A trickle charge rate is safe for indefinite charging.
  • Has individually charging AA/AAA bays.
  • The Kodak PhotoLife Charger Kit, is also available from most camera shops of 4Q2000), which includes a compact, lightweight, smart, fast (650 mA)
    compact charger and a set of 4 Kodak 1450 mAh NiMH AAs. The 110-120V fold-down wall-socket prongs on this one-piece unit make it a great
    choice for travel to civilized portions of Canada.

Do not buy a cheap charger because it is the charger that will help make those batteries work to their peak and last for many cycles and years. The rule of thumb is that you get what you pay for. Cheap fast chargers are seldom smart enough to use without careful supervision, but it is usually safe to leave your AAs in an inexpensive trickle or overnight chargers for extended periods. Just make sure the trickle charger's current is rate in milliamps (mA) and is no more than 10% of the rated capacity (C, in mAh) of the batteries you intend to charge. For example, it is safe to leave C = 1500 mAh AAs charging indefinitely in a trickle charger rated at C/10 = 150 mA or less. NiMH AAs will safely tolerate a long - term charging currents in mA up to C/10. These slower chargers generally do not need to be smart and most overnighters fall into this category.

Cheap and slow may be safe, but slow charging promotes crystallization within NiMH cells and reduces overall service life.

Smart, fast chargers are well worth the extra cost over time.

Over Charging is a No No

NiMH AAs are very hardy as rechargeable go, but overcharging is a sure way to ruin both run times and service life. Overcharging causes overheating, which literally will
cook the batteries chemistry and basically destroys them. Conditioning can sometimes reverse the symptoms of overcharging, but it's not a safe bet. Prevention is your best bet.

If the battery is often overcharged a noticeable decline in NiMH performance will be seen. Known all to well for NiCds is the "memory effect" which occurs only on abused such as over charged NiMH batteries. The "memory" can be caused by a battery which appears to have been overcharged and thus has its internal chemistry changed. NiMH batteries should never be subjected to overcharging other wise memory like symptoms will develop in their dying days.

Not All Chargers Are Equal

Have I stressed this enough yet, to try not to overcharge but if this is happening look at finding a charger which senses a full battery and will not over charge. But running batteries down to the point where it will not power your device efficiently is a good indication that it is time to recharge. When it comes to overcharge prevention, some chargers are a lot "smarter"
than others.

The smartest chargers, monitor and respond to several different overcharge indicators. When overcharging is sensed, they throttle back to a safe trickle current that NiMH batteries can tolerate indefinitely. Since fast chargers are more prone to overcharge and overheat batteries than slower ones, they'd better be pretty smart, but the really cheap fast chargers are often anything but good.

A simple charger will rely on the user to know when it is time to remove the batteries. For a slow overnight charger that starts out at a trickle (well under C/10) and stays there,
it's fairly safe to be dumb, but buying a dumb fast charger is just asking for trouble. The reality is that few of us can be trusted to babysit battery chargers, myself included.

Do not hold back when purchasing a charger. Cheap can be destructive when charging battery sets. Spend a little more and get a charger that will not over charge thus not overly heat batteries up too. Once again we know that heat destroys these batteries.

Hot Is Bad

When charging NiMH batteries heat is generated, this can not be helped, but if any of them become hot to the touch, they must be remove from the charger immediately. On average 130°F (54°C) is the maximum safe charging temperature. To the touch, normal is equivalent to hot // warm tap water.

If during charging a NiMH battery get hot, have the charger checked out or your sets have gotten mixed up or a battery in the set has gone bad. If you notice melting of any battery
parts, including the plastic jackets, discard the affected batteries immediately; an internal short is likely.

Warning: Never, ever install overheated batteries in your camera while they're still hot! There could be seriously damage to electronic equipment.

Cool Is Good

Charge batteries in a cool and well  ventilated place. If the charger has a cover , leave it open during charging.

Overnight and Maintenance Charging

When charging over night, make sure your charger's trickle current rating is in milliamps (mA) and is no more than 5 to10% of the rated capacity (C, in mAh) of the
batteries to be charged. For example, it is safe to leave C = 1500 mAh AAs on a trickle charge for days at a time in the charger at a rated of C/10 = 150 mA or less.


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