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Old Jul 22, 2002, 7:43 AM   #1
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Default Are NiMh's actually longer lasting?

Hi,

Sorry to add to the millions of existing battery questions, but I just have a small one - are NiMh batteries actually longer lasting than, say, Duracell's, or is the advantage simply that they are re-chargeable?

I've binned so many Duracells in 1 year and 4000 photos, I should consider the rechargeables - anything else I should be aware of besides getting high mAh and a smart charger?
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Old Jul 22, 2002, 2:01 PM   #2
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Nimh rechargeables last MUCH LONGER in digital cameras than alkaline batteries.
The higher the mah's the better, but then again this can also vary between different brands of batteries.
But generally speaking a good battery charger (and there are a few), and good set of fully charged nimh batteries and you will be able to shoot much longer than alkalines, plus you will have the advantage of using them over and over and over.

Good Day,
Steven
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Old Jul 22, 2002, 4:43 PM   #3
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Just to add a little to what Steven said. The days of the recharable being the underdog are long gone, the batteries you have been using can do a premature failure that is only temperary. Digicams under heavy rapid use will heat up the non-recharge causing this temp low power, when they cool power will come back. I use the Kodak rapid charger w/ 4 (1700mAh) AA's for $25 at buy.com. There are better but these exceed my needs.
Good Shootiing,
Gary

[Edited on 7-23-2002 by Gary Senkus]
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Old Jul 22, 2002, 8:59 PM   #4
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OK, let me try to explain this once and for all since this subject keep getting asked...

Alkaline battery can put out about 1A in one hour period (3rd chart down); However 1/2 way through the discharge it's voltage is already down below 1V which is unacceptable for camera use, even though it still have 1/2 of the charge left. That's explain why Gary can still use it when the cell cool down, but on other camera like the D7 the trip voltage is set at a higher 1.1V volt hence this alkaline battery last only 10 minutes or so... The Alkaline cells are still good for other use (ie flashlight) after a digital camera reject it.

NiMh can put out 1.4A (for a 1700mAh) in the same hour period, but notice how flat the 1.2V curve is. IE the voltage is constant until the battery goes off the cliff! Hence you got the full use of the entire 1.4-1.7A depending on the camera type if it can operate below 1.1V or not...

So the real difference is 10 minutes(alkaline) or 1 hour(NiMh) until the batteries become useless... Of course this is for the worst case and your mileage may vary depending on how much current the camera draw, and what its minimum voltage is set @. BTW this also explains why a battery meter indicates a true level when used with Alkaline, but when used with NiMh (or LiIOn) it shows the 1/2 way point then suddenly go kaput...


More Reading on NiMh here:
http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM

[Edited on 7-23-2002 by NHL]
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Old Jul 23, 2002, 6:33 AM   #5
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Default It's all simple math !

Let me also add this since several of my friends called me regarding their digital cameras not being able to take too many pictures... (even on NiMh diet)

I use the microdrive and can take several hundred pictures with my battery hogging D7 on a single charge, while my friends using battery-friendly flash achieved less!!!

Well when a picture is taken, the camera processes the image then does a SINGLE write. When reviewing and deleting a picture (a 128Mb CF can only hold 50 frames), a person actually makes his camera do a display, two memory accesses: a read AND a write (ie two shots lost!), and another read for the next picture display (another shot lost!). On super-fast camera like the D7 where thumbnails are not stored, a person displaying the pictures in a 3x3 matrix actually make the camera perform 9 pictures reads, hence compounding the problem. Yes, deleting pictures are free, but you are taking a free-ride from the battery... and even though the microdrive takes more power, people are wasting more juice by reviewing and deleting pictures in a smaller flash card... (not counting navigating the camera's GUI menu, which all use power!)

[Edited on 7-23-2002 by NHL]
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Old Jul 23, 2002, 2:20 PM   #6
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NHL,
I am thinking about getting a micro-drive for my digital camera. Perhaps the 1Gb capacity drive.

How do you recommend? Definitely get it? Or what until price comes down a little?

Thanks,
Bowisc
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Old Jul 23, 2002, 2:36 PM   #7
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Both MonsieurMS and I are on our 2nd 1G. How low do you think it'll go? I believe it's already dirt cheap @ under $240/1G...
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Old Aug 3, 2002, 10:46 PM   #8
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While I have posted this info before on the old Forum. The subject of batteries charging always come back, and I hope this posting will help new readers just like my FLASH posting did when I reposted it.

While NiCad charger has been around a long time, NiMh can not be recharged with a NiCad constant voltage battery charger. This is because as the NiMh cell heats up under charge, it's voltage decreases and requires a charger to put out more current to compensate, which again will heat the cell even further until one has a run away condition that will then damage the battery.

NiMh are normally charge with a constant current: A slow (trickle Charge), or overnight charger can charge a NiMh cell indefinetly (0.1C to 0.3C) without damaging it (ie one can leave the cells plug into the AC wall outlet with the charger). This is also how series batteries or battery packs are charged (PowerBank and others).

Fast chargers however, an hour or less, charge NiMh at a very high constant current (3C or higher) need to monitor individual cells for end of charge. They detect this condition by design with an internal microprocessor by detecting one, or ALL of the following parameters, and switch to trickle charge:

o dT/dt - Change in rate of temperature change
o -dV - A slight drop in volage when a cell is charged
o High temperature limit (ie the battery is geting too hot!)
o Time limit (ie can not charge @ high current forever, some thing is wrong!)

This also explain why some chargers (ie Rayovac and Maha) charge better than other because each cell is placed further apart from one another reducing the heat built-up, and some chargers actually undercharge because their owners fail to open the lid/cover. The placement of the charger also has a lot to do since (open space is prefered) in a tight corner the temperature rise might fool the charger into trickle charge, and then its owner wrongfully accused his camera as a battery hog when the NiMh batteries are not yet fully charged (ie they now require at least overnight to complete) !!!

http://www.gpbatteries.com.hk/catalo..._technical.pdf

This also explain why some users only reach the full capacity of their NiMh only after several usages... They did not charge their cells fully in the 1st place !!!

[Edited on 8-4-2002 by NHL]
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