Batteries - what type?

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James Sweet wrote:

I've seen it with NiCads. You charge one and it appears to be discharged after brief use. Then you put it in a holder with a 2-ohm shunt, and it keeps producing current, but the voltage is low because the internal resistance is high. With the high internal resistance, it may take a long time to discharge completely. Completely discharging gets rid of the high resistance.
It appears that if a NiCad is left charged or partially charged for a long time, a chemical change will cause high resistance in the charged part, but discharging will correct it. Lead-acid seems the opposite; if it is not routinely fully charged, the discharged part will develop high resistance, which can be corrected by fully charging, which can take a long time due to the high resistance.
NASA says NiCads should be drained and shorted if not needed immediately. When you get ready to use them, the first step is to overcharge them, 40 hours at C/20.
Sometimes a NiMH may not charge fully. I think that's from gas bubbles and not memory effect.

In my experience, keeping a NiCad charged eventually results in memory effect, which can be corrected. If you removed one of your batteries, I wonder if it would provide 8.2V across 150 ohms for a couple of hours. If it won't, that could be memory effect.
In my experience, slow or trickle charging NiCads causes electrical leakage and eventually shorting. Internal electrical leakage can be detected by testing capacity after two weeks off the charger.

I think the heating comes from the gases recombining. I wonder if the heat can damage a cell even if there is no venting. (I like to check temperature with an infrared thermometer.)

Are C/10 and trickle charging really recommended for NiMH? In my experience, both kinds of cells do better if I stick to microprocessor-controlled fast chargers.
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My experience with both kinds of batteries is that if I remove a set from service and let it sit idle for more than a few months, they'll be ruined. Every time.
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I have three "power-off" lights that are dead because the batteries have died. They take two AA batteries which I want to replace. Which type would be the best - Lithium, Nickel-Cadmium, or Nickel Metal Hydride? They would be plugged in and constantly charging until the power goes off.
---MIKE---

>> (44 15' N - Elevation 1580')
RTFM and follow. Really. My first suggestion would be NiMH, as I have good luck with them on my cameras and they save a lot on disposable alkalines. But each, alkaline, NiCd, and NiMH have different operating characteristics related to slow draws, the curve when they pass a certain use point, and just things individual to each. I'm sure that the directions may clearly state that you could use any kind, or specifically if there is some type you should NOT use. I'd trust the manual more than anyone here.
Even me.
Especially me.
Steve
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I have three "power-off" lights that are dead because the batteries have died. They take two AA batteries which I want to replace. Which type would be the best - Lithium, Nickel-Cadmium, or Nickel Metal Hydride? They would be plugged in and constantly charging until the power goes off.
---MIKE---

>> (44 15' N - Elevation 1580')
You are betting your life and the lives of others on these lights functioning. Don't accept any half baked ideas you might get here. Read and follow the manual.
In my life, there has been many an item that specifically said what battery to use and which not to use. I have ignored or just not read these statements. They weren't things, though, that were life-saving devices, so my poor reading skills didn't make a very big difference.
This can make the difference in life and death. Be sure.
PERIOD.
Steve
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SteveB wrote:

Talk about overly dramatic. These aren't built in emergency lighting in a commercial building, but rather cheap plug in power outage lights that you can buy in drugstores. They are not lifesaving devices any more so than a dollar store flashlight tucked in the nightstand. Manual? They might have had some instructions for use on the back of the package, if you're lucky, but none of mine ever said anything about the battery, it wasn't even meant to be user replaceable and weren't even name brand, just cheap generic AA NiCDs. I've had a couple similar lights, they seemed like a good idea and were handy at times, but hardly fail safe, and half the time they turned out to be broken by the time they were needed. Now I just keep flashlights stashed in convenient locations.
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