NiMH Rechargeaable Battery Advice

[alcain Profile Private messageWebsite]

Hi folks. Any of you using NiMH Rechargables? Many of the newer digital cameras use them as well as virtually all pro speedlight flash units. I have recently been experiencing problems with some of my batteries and went on a self guided college course on NiMH (nickel metal hydride) batteries. Here is what I learned...

THEY COST A LOT BUT SAVE YOU A BUNDLE

Rechargeable batteries are used in cameras, camera flash, remote controls, etc, etc. and although they are quite an expensive outlay together with a suitable charger, they will nevertheless save you a bundle of cash because they can be used 50 to 500 times over, depending on the brand. If you compare the cost of 100 penlight batteries with the cost of 1 rechargeable battery, you will start to see the savings. They come in various sizes: penlight (AA and AAA), C & D sizes) , square 9V types and others as well.

AN EXAMPLE OF SAVINGS

Usually a set of 4 rechargeable penlight batteries (size AA) with an included charger, will cost about 10 times what a pack of 4 non-rechargeable AA batteries cost.

Non Rechargeables x 4 = $1.80 After replacing the batteries 50 times: $90

Rechargeables x 4 + charger = $18 After replacing the batteries 50 times $18 (plus about $2 electricity costs)

So you would save at least $70 over the lifetime of just 4 rechargeables. But newer rechargables may be charged
from 300 to 500 times - a savings now of over $540.00!!

CAN YOU USE RECHARGEABLE BATTERIES IN ANY DEVICE THAT TAKES BATTERIES?

Yes. They will work fine in any device that they fit into correctly.

WHAT DOES NiCd AND NiMH MEAN?

NiCD stands for Nickle Cadmium and is an older technology. NiMH stands for Nickle Metal Hydride and is a newer technology with a number of benefits.

It can be recharged more often.

It does not suffer from the "memory effect" so it can be recharged when it is only slightly "used" or discharged with no ill effect. The NiCD type like to be fully discharged before being recharged.

It can hold more charge so it will last longer before needing a recharge.

These batteries are rated in mAh, or milli amp hours, usually printed on the side of the battery. eg: 2600mAh. This is the amount of charge they can hold. A 2600mAh battery will keep your device going for longer than a 1700mAh battery.

HOW LONG WILL A RECHARGEABLE BATTERY LAST?

Some of the lower quality brands will allow you to recharge them 30 or 50 times, while quality brands will allow 300 or more recharges before the battery starts to underperform. (Some boast of 1000 recharges; but take this with a pinch of cynicism!) This normally means a year to 4 years before you have to replace the batteries with new ones.

HOW LONG CAN THESE BATTERIES BE STORED BEFORE USE?

The new NiMH batteries now have a technology called low discharge which allows the batteries to be stored on the shelf (or in your camera bag) for longer periods. In six months they will only lose 15% to 20% of their charge, compared to standard NiMH technology which loses up to 15% in the first 48 hours PLUS up to 2% per day thereafter.. Older types of NiMH batteries have to be recharged every few weeks if left on the shelf.

ARE THESE BATTERIES ENVIROMENTALLY FRIENDLY?

They are mercury free but still need to be recycled. But they are definitely more environmentally friendly purely because there are less of them to dispose of: in the example above: 4 as opposed to 400 of the non-rechargeables for the same amount of use.

So, make the switch to rechargeables and save yourself some cash and a lot of trips to the store!

What I have done in my work flow:

I have learned from (expensive) experience, that Duracell batteries are sorry in quality control. Some are great while others (new, out of the package) are severely lacking in the ability to hold a proper charge.

Energizer now sells 2300mah LSD (Low Self Discharge) batteries which seem to work much better for me.

I NEVER use a fast charger (One hour or less charging time) as these literally COOK the batteries and will make them wear out in as few as 20 charges. A four hour charger is safer, but an 8 hour charger is best for the batteries.
Look for the rated MaHR rating of the charger: NEVER use one rated at over 700Mah. It will be printed on the label somewhere. A 360Mah charger is common and will serve you well.

Also, look for a "smart" charger (One that charges the batteries individually) This charger will typically have a led above EACH battery compartment instead of just ONE led saying all batteries are full. These "dumb" chargers will stop when any ONE battery is full. leaving the rest undercharged. Energizer makes a cheap smart charger that does charge all four batteries individually (but as a set in the charger).

The best chargers cost more but have a big payoff. I have two LaCrosse BC-900u chargers. They are "smart" chargers and give individual readouts in actual numbers for each battery. They can re-condition worn out batteries and have adjustable charge rate settings. But they can also tell me which batteries are keepers and which ones are ready to be re-cycled.

I also label my batteries in sets of four. I use these "sets" as sets for my flashes. Keeping them in sets will lengthen the lifespan of the set as a whole.

I never leave batteries in any of my flashes. I do leave my LITHIUM non-rechargables in my slave units, as they are extremely safe.

Most importantly of all, is - I charge any batteries I plan to use the day before any photo shoot, and have three extra sets available (as well as an emergency backup pack of four (expensive. but with a shelf life of fifteen years) lithium batteries.

Since I have been paying more attention to the care of my rechargables. I now feel more confident and am having better results with them.


FOR THE GEEKS:

NiCad and NiMH batteries are amongst the hardest batteries to charge. Wheras with lithium ion and lead acid batteries you can control overcharge by just setting a maximum charge voltage, the nickel based batteries don't have a "float charge" voltage. So the charging is based on forcing current through the battery. The voltage do do this is not fixed in stone like it is for the other batteries.

This makes these cells and batteries difficult to charge in sets of two or four. This is because you can't be sure that each cell is the same impedance (or resistance), and so some will take more current than others even when they are full. This means that you need to use a separate charging circuit for each cell in a charger, or balance the current in some other way.

The coulometric charging efficiency of nickel metal hydride batteries is typically 66%, meaning that you must put 150 amp hours into the battery for every 100 amp hours you get out. The faster you charge the worse this gets.

The minus delta V bump that is indicative of end-of-charge is much less pronounced in NiMH than NiCad, and it is very temperature dependent. To make matters worse, new NiMH batteries can exhibit bumps in the curve early in the cycle, particularly when cold. Also, NiMH are sensitive to damage on overcharge when the charge rate is over C/10. Since the delta V bump is not always easy to see, slight overcharge is probable.

As the battery reaches end-of-charge oxygen starts to form at the electrodes, and be recombined at the catalyst. This new chemical reaction creates heat, which can be easily measured with a thermometer.. This is the safest way to detect end-of-charge during a fast charge.

Overnight Charging

The cheapest way to charge a nickel metal hydride battery is to charge at C/10 or below (10% of the rated capacity per hour). So a 100 mAH battery would be charged at 10 mA for 15 hours. This method does not require an end-of-charge sensor and ensures a full charge. Modern cells have an oxygen recycling catalyst which prevents damage to the battery on overcharge, but this recycling cannot keep up if the charge rate is over C/10. The minimum voltage you need to get a full charge varies with temperature--at least 1.41 volts per cell at 20 degrees C. Even though continued charging at C/10 does not cause venting, it does warm the battery slightly. To preserve battery life the best practice is to use a timer to prevent overcharging to continue past 13 to 15 hours.

Faster Charging

Using a timer it is possible to charge at C/3.33 for 5 hours. This is a little risky, since the battery should be fully discharged before charging. If the battery still has 90% of its capacity when the timer starts you would have a good chance of venting the battery. One way to ensure this doesn't happen is to have the charger automatically discharge the battery to 1 volt per cell, then turn the charger on for 5 hours. The advantage of this method is to eliminate any chance of battery memory.

Fastest Charging

If a temperature monitor is used NiMH batteries can be charged at rates up to 1C (in other words 100% of the battery capacity in amp-hours for 1.5 hours).

I do use a fan to cool my batteries when charging them. I made a nice cooling fan from a spare CPU fan wired to an old 12v power adapter. I just position the fan over the batteries.

Here is my setup:


Hope this is of some help.

Regards, ~al

[northward Profile Private messageWebsite]

Thanks Al for this thorughly researched contribution!
Wolf

[nannybear Profile Private messageWebsite]

Great stuff Al. I have been using only rechargeables for many years now...and love them.

[gpsmikey Profile Private message]

Good info Al - be aware that the LaCrosse model you mention has had issues in the past with meltdowns. From posts I found, the later versions of the firmware (V34?) have done much better since it set the cut-off temp to a lower value, but there have been reports of the melting. I would still seriously consider getting that charger, but I would make sure I did not leave it unattended while it was charging. Some additional information if anyone is interested in battery types etc.
http://www.batteryuniversity.com/partone.htm

mikey

[texbrandt Profile Private message]

Have you done any testing with the lithium batteries? After trying the NiMH batteries with a Kodak point and shoot I finally had to go to the lithium, the NiMH voltage at 1.2 v. was not enough to run the camera very long even fully charged. The lithium rechargeable cost a bit more, but so far I have been well pleased with their performance.

Robert

[alcain Profile Private messageWebsite]

Robert,

The lithium (non-rechargable) batteries measure 1.5 Volts.

NiMh batteries (AA types in this example) typically have 1.2 Volts for much of their useful life. Apparently Kodak designed these cameras to determine that a battery is depleted when the Voltages gets close to 1.2 Volts per cell, thus NiMh batteries seem to deplete more rapidly than common. For example, a pair of charged NiMh AAs seem to last just a few shots in your camera but they can be moved to a different camera (different manufacturer) and the same batteries will continue for dozens of shots.

Alkaline batteries start out at slightly higher than 1.5 Volts and gradually decline (if not loaded too heavily). Problem is that Alkaline cells (AA in this example) cannot deliver the amount of current (power) that your camera requires without rapidl Voltage decline.

Lithium would be the best choice in your case.

Regards, ~al

[alcain Profile Private messageWebsite]

The later versions of the firmware (V34?) have done much better since it set the cut-off temp to a lower value, but there have been reports of the melting. I would still seriously consider getting that charger, but I would make sure I did not leave it unattended while it was charging.

Good info Mikey. If you will note that in the photograph I supplied, I use two safety precautions. (I have never had a meltdown, and have been using these chargers for over a year now).

1. I place my units on a ceramic tile with insulated feet underneath.

2. I place an old CPU fan (in a home made stand) directly above the chargers which blows a constant stream of air over the batteries - they don't even feel very warm, even when charging at 700ma.

My units both have V35 installed firmware.

I leave mine unattended all the time, but feel ok with it due to the safety precautions I use.

Thanks again Mikey!

Oh, by the way - (you will appreciate this) I do use my FLUKE 561 HVACPro IR Thermometer to check my battery temps. Usually with the fan running, at a 700ma charge, the temp never goes above 85 degrees - far too cool to even melt candle wax.

~al

[gpsmikey Profile Private message]

"Oh, by the way - (you will appreciate this) I do use my FLUKE 561 HVACPro IR Thermometer to check my battery temps. Usually with the fan running, at a 700ma charge, the temp never goes above 85 degrees - far too cool to even melt candle wax."

Very good - it is important to let the budget director observe you using your new toys ... I mean tools so they understand they are important I was using mine a while back to figure out which cylinder on the truck was not firing correctly (you can't easily get at the plug wires). Put a load on the engine and looked for the cool port on the exhaust (made sure the wife saw how well that worked ! ).

The melting problem seems to be fairly isolated, but several people reported it happening - the conditions seemed to be - the battery not properly touching the temperature sensor AND earlier versions of the firmware that had a cutoff of somewhere around 160 degrees F apparently. Newer versions of the firmware reportedly have the cutoff temperature significantly lowered (although I prefer to do it like you with a fan - I don't like running batteries that hot).

mikey

[alcain Profile Private messageWebsite]

Mikey...

When I grow up, I want to be just like you!


~al

[sheldonk Profile Private message]

Hi Al,

Great info! I switched over to nimh AA last year. I use the same charger you show in the picture on the left. I don't do any fast charging so cooling hasn't been a problem.

I really like the Sanyo Eneloops. They hold a charge for months and months as you mention in your article. I use them in TV remote controls, wireles keyboards and my sons Wii controllers. I used to find if you used plain rechargable batteries in remotes, you had to remember to recharge the batteries every few weeks. With the Eneloops, I go months before I have to swap out remote control batteries. I bought a few extra sets and keep some fully charge on hand at all times. After doing a swap, I immediately recharge all the batteries I swap out and I'm good to go again!

Cheers!

Sheldon

[alcain Profile Private messageWebsite]

Thanks Sheldon. One day I will try the Sanyo's. The reviews are always awesome.

Regarding the LaCrosse BC900u...

I can't emphasize this enough. The one feature about this unit that makes it indispensable is this:

The ability to accurately calculate the TRUE capacity of a NiMH battery.

I was buying Duracell 2600mah batteries because they were on sale at Home Depot...

but I was having issues with my flash units not re-cycling fast enough...

I ran three sets of four batteries through the "test" mode and discovered why...

On all three sets, none came up to the true 2600mah specs as labeled on the battery.

But the astonishing part was that IN EACH SET, there was one battery that tested below 1200mah,
in one set the bad battery was only 830mah. These were brand new Duracells 2600mah.

Here is how it works using NiMH batteries in a device...

The device will only have as much total power as the battery with the LOWEST mah rating, therefore - my flash
was re-cycling slowly because I only had 830mah in that set instead of the 2600mah!

ALL of the LSD (Low Self Discharge) Energizers I purchased (2300mah) tested ABOVE 2400mah right out of the package.

SHAME on you, Duracell...


Regards, ~al

ps: from a review on the web...

After testing a number of the newer 2300 mAh-labeled cells, the Energizer 2300s are the current leaders for total power, although the Powerex 2300s run a close second, with only 2% lower capacity. Now that I've revived my battery testing program, I have a number of other cells in-house and currently undergoing test, and hope to post another update in a month or so, with results from cells with labeled capacities as high as 2500 mAh. (I have to admit that I'm more than a little skeptical about some of these, we'll see how they hold up through multiple charge/discharge cycles.)

[sheldonk Profile Private message]

Thanks again Al!

Very interesting about the bad batteries you discovered. I really have to sit down and read the manual from the charger. It's long and the print is small. Looks painful to go read, but it's time to figure out how to do all the cool stuff this charger can do! That is why I bought it!!!

Sheldon

[alcain Profile Private messageWebsite]

Sheldon, here is a quick start on testing true capacity...

UNPLUG the BC900u

Insert the four batteries you wish to TEST.

Plug the charger back in.

Within eight seconds, hold down the MODE button.

Click it several times, you will see a menu of available modes.

Choose TEST.

Now click and hold the Current button.

It should show 100ma, click on it until you see 200am (this will speed up your test time by half).

It might take up to 10 hours (or more) using 200ma on 2500mah batteries as the charger first charges the batteries, then dis-charges them (this is where it finds capacity), then re-charges them up for you again.

I use 350ma when in test mode and here is why... the discharge rate will always be one half of the charge rate.
Therefore, when testing in the 350ma rate, it charges back at 700mah.

In your case, if you choose a test rate of 200ma, you will re-charge them back at a safe 400ma.

When done, you will be able to read the true capacity. If above 1amp, it will use a decimal as in 2.30a (2300mah)
if less than 1 amp or so, it will read as maybe 1200mah (1200mah - less thanj half of the labeled capacity)

You can try the "Refresh" mode which will attempt to recover a bad cell, but it takes up to two days and usually a cell
is unable to recover - some do, don't get me wrong.

Hope this helps, ~al

[gpsmikey Profile Private message]

Interesting information although your comment on recycle time is not quite accurate - the mah capacity of the battery will determine how many shots you can get from the battery, however, what determines the recycle time is a function of the internal resistance of the battery. That is one of the problems with alkaline batteries in bigger digital cameras - as they discharge the internal resistance goes up and the battery can no longer supply the required current for a short period of time. You may only get 20 shots on alkaline while you may get 150 on the NiMH. If you take those alkaline that can no longer power the digital camera (that often wants more than 1 amp peak) and put them in a low current device, you will find they still have as much as 70-80% of their power remaining, they just can't supply the short term current due to the increased internal resistance. Same thing happens with the lead-acid battery in your car when the battery dies (not when you leave the headlights on - that just runs the battery down). Typical lead acid battery failure is the sulphate builds up to where it shorts one cell out and discharges it. Now, instead of a 12 volt battery, you have a 10 volt battery with an open cell in the middle (a fully discharged cell is almost straight water). On the older batteries where the buss bars were on the top of the battery exposed, you could short the dead cell and still start the car when that happened - now you can't get at the inter-cell connectors with the new ones. Used to be a similar problem with the old transistor radios everybody had that used a 9 volt battery. Remember how garbled it started to sound as the battery ran down ? Put a decent electrolytic capacitor across the battery so the internal resistance (to the ac signal - the ground return) dropped down and you could get hours more listening time out of the "dead" battery.

So much for today's trivia lesson I guess - not enough sleep last night - new puppy in the house

mikey


mikey

[sheldonk Profile Private message]

Thanks Al!!! I will try that.

Sheldon