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04-16-2009, 01:11 PM   #1
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Join Date: Apr 2008
Location: Fremont, California
Posts: 39
Experience with AA NiMH rechargables with my ist DS/DL cameras

I primarily use AA NiMH rechargables with my 2 DS's and a DL when I am in my home base. "Home base" is when I am at or around home, with easy ability to recharge back at home. In the home base, my camera usage is off-and-on; I would take 10's of shots and the cameras would sit for days in my bag.

(When I am out of my home base, I use Lithium or Alkaline. I do not carry any charger with me in the bag. That was a decision I made when I went with DSLR and PS cameras based on AA format.)

I have 6 sets of AA NiMH batteries all together. Most of them I purchased. The RadioShack set was acquired through one of my DSLR purchases.

1. Sony 2700mAh (2007)
2. Sanyo 2100mAh (2007)
3. Sanyo 2100mAh (2007)
4. RadioShack 2000mAh (2008 acquired used)
5. Sanyo 2500mAh (2008)
6. Sanyo 2500mAh (2008)

Chargers I use:

Sony BCG-34HRMF "faster" charger (4X 525mA) - charges min 1 max 4 batteries in about 3 hours. Has a refresh function, where the battery is first discharged and then charged. Some monitoring capability.

Sanyo NC-MQN4U "slow" charger (2X 250mA) - charges min 2 max 4 batteries for 16 hours or so. No monitoring capability.

After a couple years of use, one after the other, sets 1,3,5,6 started to show signs of weakness. The sets delivered very little usable time in the camera. Upon initial insertion right after a charge, the DS/DL battery indication would show full battery bar. Upon using the camera a short time, the battery bar would go down to half bar. Again after some more use, the battery bar goes to no bar and soon lock me out from using the camera.

(All the while, sets 2 and 4 functioned flawlessly. They hold charge for a long time over my off-and-on usage in the home base.)

The "short time" became shorter and shorter with those weak sets, no matter how I charge them. I tried the refresh function on the Sony charger; I tried slow charging with the Sanyo charger. Both method showed very little improvement to the battery performance.

I was getting frustrated and was ready to give up on these, and go eneloop. ( I did buy a set but am holding off deploying the eneloop. I want to get a better understanding of the NiMH's.)


A couple of months ago, I began to look into what was going on with these sets.

I built a simple load test. It consists of a single AA holder and a flash light bulb holder with a bulb that will draw about 250mA from 1 battery. I used a digital voltmeter to measure the voltage across the battery with and without the load. (All parts from RadioShack)

What I found is that, in all of the weak sets, there is 1 or 2 battery that were consistently weaker. Without load, the voltage across the battery showed the same as the others. But with load, the weak battery showed at least 1/10th of a voltage lower that the others. Probably enough to cause the ist's to stop functioning. ( For sure, the ist's have a higher requirement of battery voltage. My Canon PS using AAs, will operate happily with the weak sets. )

Further I found that this condition progresses. Something is going on with these cells. I think some of these cells goes into a "chemical" state that deteriorates their capacity.


Recently, I saw the LaCrosse BC-700 charger on sale on Amazon for $25. I purchased one and gave it a try.

This charger has a function called "refresh" that is unlike the Sony charger's. In this mode, the charger will cycle through discharge and charge, while monitoring the charge capacity of the battery. It will stop when the charge capacity cannot be improved any more. So this "refresh" function can go on for 1 day or 2, but you don't have to do anything. The charger does it all by itself. I just monitor the data on the LCD.

In the beginning of the "refresh" cycle, I saw that the charge capacity of the weak batteries were low. For example, the 2500mAh battery would be showing like 1000+ mAh. But as the "refresh" goes on, I could see that the capacity started to climb and the cycle would be completed when the capacity stops climbing. In all cases, the 2500mAh batteries stop at around 2500mAh and the 2100mAh at around 2100mAh. Amazing!!


I have started to re-use these "refreshed" battery sets in the DS/DL's in my Home Base. It has been 10+ days since, and so far so good.

04-16-2009, 05:45 PM   #2
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Join Date: Jan 2009
Location: SE Connecticut
Posts: 38
NiMH Chargers

I was originally using a Radio Shack 23-427 to recharge my Ni-MH batteries. Besides being very slow (13 hour charge), the batteries started giving me fits after a couple of years.
Bought the Sony BCG-34HRMF. It's like 4 quick and smart chargers in one. If there's a cell it doesn't like, it tells you so. I ended up junking about 25% of my Ni-MH cells and replacing them, but I'm now a happy camper. I'm junking the Radio Scrap charger too.

Al
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