Which NiMH cells for a skeptic?

I'm a longtime NiMH avoider. I don't inherently like NiMH due to bad experiences in the past with them (though with notebook computers, not lights) as well as hating the self-discharge aspect. I often keep lights in the cabinet for a month or two at a time without using them, and don't want them to be dead when I finally grab them! I also don't want to have to swap batteries as the first thing I do when I grab a flashlight. /ubbthreads/images/graemlins/frown.gif

You're all (mostly) so high on NiMH, though, that I'm willing to give them another chance. /ubbthreads/images/graemlins/smile.gif And I wanna save money on batteries! But I'll be one step away from abandoning them right from the start -- just being honest here -- so given my scenario, which NiMH cells (specifically... brand, model number, etc.) should I try as my guinea pigs? I want something with minimal self-discharge and maximal ability to power lights with fairly high current demands if necessary.

Suggestions, please?
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The NiMHs are great to save money, but have all the downfalls that you mention. They ARE NOT for use in things that you put them in and then put whatever it is away for months at a time. I use them in my digital camera and lights that I carry and use everyday. I recharge them at least once a week, usually more often. You get more cycles when they aren't completely run down. The charger is at least as important as the cells for maximum use from the cells. I don't think that there's much argument that the Maha PowerXs are at the top of the chart. But I'm not willing to pay $4+ for a cell. There's a recent chart showing the rating of cells with a reference to it somewhere on this forum. The Nexcell 2100s that I use are rated 5th (or 3rd depending on how you read it) and can be had from Battery Station for $1.50. I bought a bunch to get a good price and need to sell some of mine off too. With a good charger (overheating is a killer), you get 500 - 1000 cycles. If you were to charge them EVERY day, that's a year and a half to 3 years use. From my personal experience, I recommend the the new Maha 401. It's about $40 and you can buy it bundled with Maha batteries at about $2.50 each.

In short, NiMH are great except for the high discharge rate. If you can make regular recharging fit your lifestyle, you'll love them.

Yah, they're definitely not good for items that sit around unused for long periods of time. For those, use regular primary cells, alkaline or lithium.

or Li-Ions....

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Kitelights, great info with all the specifics I wanted, and no hype. Thanks! /ubbthreads/images/graemlins/grin.gif

Highlandsun, that's one reason I've gotten into lithium AA cells over the years, despite their relatively high cost. I've learned to use them for three things: (1) high current drain; (2) poor man's regulation of an otherwise unregulated light; and (3) things that will sit around for months between uses. They haven't let me down yet!

Believe it or not, I don't think I've completely drained any of the lithium AA's that I've deployed... at least not yet... /ubbthreads/images/graemlins/ooo.gif /ubbthreads/images/graemlins/smile.gif

(I use alkaline AA's for most other purposes due to dirt cheap cost in bulk. I do use some other cells and lately have gotten into CR123A-based lights, but still, for the most part, our household is standardized on the AA format to simplify things.)

Phaserburn, funny you should mention it... /ubbthreads/images/graemlins/wink.gif

Me too. Low-frequency-of-use has detered me from going with rechargeables. But I am approaching a cusp. I'm putting together a 32 watt light which will chew up 8 CR123s and a lithium AA to boot -- in just 35 minutes. That's $20 per hour! If I ever get it working right and begin to use it even a little, I have to go with NiMHs.

I will second a good charger is VERY important. When I first got back in to NiMH I was about to dump them again, then I found the Maha charger. It about doubled the run time on the same batteries, amazing!

In any case a good read is at
http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM

And while you're at the Imaging Resource, you should check out their Great Battery Shootout. It's a pretty comprehensive review of AA NiMH cells available in the market.

I agree with kitelights about price: I get my Sanyo 2100s for about $1.70 each, but the Maha 2200s would set me back about $3.50 each. The small capacity gain isn't worth it for me.

[ QUOTE ]
PaulW said:
Me too. Low-frequency-of-use has detered me from going with rechargeables. But I am approaching a cusp. I'm putting together a 32 watt light which will chew up 8 CR123s and a lithium AA to boot -- in just 35 minutes. That's $20 per hour! If I ever get it working right and begin to use it even a little, I have to go with NiMHs.

[/ QUOTE ]

Okay, I'll ask... what are using as light source(s) to reach 32 watts?

Brock, which Maha charger do you have?

All, how do you know when the NiMH cell is completely spent (in other words, not useful anymore); does it suddenly not hold a charge, or is it more of a gradual dropoff of capacity with each recharge?

I have the 401 now, best you can get for AA's and AAA's as far as I am concerned. I started with the 124, then the 204 and now the 401. The 204 is good, but you have to charge in pairs. I prefer individual cells so you know if one is bad or if you use an odd number in anything.

Milky
The dropoff is sharp. That is one of the advantages of NiMH (and NiCads) that they run very flat, but when they drop, they drop quickly. And the danger in that is that you can reverse charge them, essentially ruining your cell. When you notice even the slightest drop, change them out and recharge. Even better, recharge them long before you NEED to. You get much more life out of them by recharging before you suck them dry.

Get in the habit of topping off your cells. If you have some that have been laying around for even a week or two, top them off before you use them. With a charger like the 401, it'll only take 10 - 20 minutes and you'll know that you're starting out with fully charged cells.

Ooops. I didn't read Brock's post properly, and thought he posted a link to the review of the charger. /ubbthreads/images/graemlins/crazy.gif My bad on the double link...

Anyway, Imaging resource does have reviews of the C-401FS as well as the older C-204F.

Kitelights, I wasn't very clear, I'm afraid; I meant how do you know when the NiMH cell is PERMANENTLY spent, as in finished with its service life... it's been charged 500-1000 times (or whatever) and is ready for the trash can? Does the cell suddenly refuse to charge, or is it more like the capacity gradually decreases, charge by charge, until it's no longer a useful amount? /ubbthreads/images/graemlins/icon15.gif

Incidentally, the info you did provide was quite useful, too. /ubbthreads/images/graemlins/grin.gif

All, this Maha C-401FS charger sounds pretty good. The review said the quick charge (which at 100+ minutes doesn't seem all that quick!) might shorten the life of the batteries. In practice, though, should I care? If we're talking about the battery lasting "only" 700 cycles rather than 1000, for example, and replacement NiMH cells available for $2 or less each, I would be inclined not to worry about the shortened life...

Also, how long can cells be left in trickle mode on the charger? Here's where NiMH works against me, but maybe you folks have a suggestion: I charge my cells ahead of time because I often don't have 100 minutes to sit around when I realize I need fresh cells... but if I have to remove the fresh cells from the charger right away, they'll sit around and self-discharge until I get around to using them, and I may have half-dead cells! If they could sit in the charge indefinitely, for me that would be a HUGE win; just grab 'em and go. That's what I do with my StarTAC cell phone batteries (Li-Ion), always keep one on the charger, one in the phone. Then swap as necessary. Works great /ubbthreads/images/graemlins/smile.gif

Can I use the "swap" strategy with the 401FS charger, or will I kill my NiMH cells leaving them charging for that long? If I can't do it with this charger, is there another that's smart enough, perhaps, to stop charging completely, then periodically top off the cell as necessary?
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If you are looking for 2100s at a good price try Walmart. I bought a 4 pack of Energizer 1200mah NIMHs for just under $10.00. John

Lucien /ubbthreads/images/graemlins/wink.gif The more we post that link the better /ubbthreads/images/graemlins/smile.gif

Scott I have three sets of 4 we use in our digital camera (Dimage D7). What I do is when the camera says they are low I swap them out for the spare set in the camera bag. Then I take the dead ones out and put them in the 401 (on slow charge) and let them sit. The ones that were in the 401 go in the spare set in the camera bag.

I have let them sit in the 401 for over a week. It doesn't seem to hurt them at all. They aren't warm at all, but they are fully charged.

If we are going on a trip I charge them all again, whether I just took them out of the charger or not. NiMH's like to be charged rather then sitting. I charge my spare AA's at least every other week. I primarily use the slow setting because I have so many spare cells and they just sit in the 401's. On vacation or if I have a lot to charge I do switch over to the 100 min charge.

I should add if I take them out of my camera on a slow charge it is about 3 to 4 hours, and it is always less then an hour in fast mode. I would guess the 100 min rating is for truly dead batteries.

If you drop a cell that has been sitting for a month it will take about 20 min to top it off, it is about 10 min after sitting a week.

Are there any reviews that compare the self-discharge behavior
of different brands of NiMH cells? I've noticed pretty
significant differences - I have some AAA cells that will
go practically dead in a week (unused, or in a PDA that is
'off' all of the time) while the "brand name" AA cells I have
in the digital camera show a suprising amount of life left
after a month sitting in the camera...

billw

Scott-
I can't really answer your question about how do you know when they're dead, because I haven't had one "die" yet. I've been using NiMH for at least 3 years, maybe 5. If they behave like NiCads, then you will notice a drop off in capacity and their ability to hold a charge. If the cell is in any way defective, the 401 senses it and the LED will blink (and won't charge it).

The trickle charge on the 401 is 50mA and, from what I've read, is considered "safe" for a continuous charge. I personally don't leave mine in for extended periods, mainly because as Brock pointed out, the top off time is so short (10 - 20 minutes).

Li-ion technology isn't quite the same (wouldn't it be nice?). Motorola told me only to expect 12 - 18 months life on a Li-Ion pac, but I've personally had them last more than twice that. And isn't it ironic that that you can leave them in a charger indefinately and yet they have the lowest discharge rate. I've used a pac that hadn't been charged in a year.

Kitelights, I heard somewhere that Li-Ion cells like to be recharged frequently; that complete discharge is what shortens their life. From my own experience that seems to be the case. As I said earlier, I keep one of my StarTAC batteries on the charger at all times, and every time I return home I swap the battery in my phone with the one in the charger. Do the same with my (Li-Ion) digital camera. My wife, on the other hand, lets her cell phone battery die before putting it on the charger, which is a continuing annoyance for me.
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The success with Li-Ion is the reason I'd like to handle the NiMH similarly, with some batteries always on the charger, ready to go... and the batteries are cheap, I know, but still I'd rather not inadvertently kill them if it could be avoided. Having some instantly available just works so well for me! /ubbthreads/images/graemlins/grin.gif

I'm somewhat disappointed with Motorola's battery-control logic. The fact is that LiIon self-discharges slowly, and doesn't take well to trickle charging. Once it's fully charged, any more power will damage the cell. With my StarTac charger, the charge circuit shuts off when the pack is full (good) but it doesn't monitor self-discharge. So even if I leave the pack in the charger all the time, if it's been sitting idle for a month or so, the pack will no longer be fully charged - after the pack is full, the charger shuts off and doesn't check to see if a topping-up charge is needed later.

Also I recall that LiIon technology will handle 500-1000 cycles, period. Charging at partial or empty charge makes little difference. In a cellphone application, "empty" is relative; the phone stops working at 3.1V or so, but the LiIon can provide energy on down to 2.5V. So even when you let the phone run the pack down "all the way" it hasn't done any harm to the LiIon cell at all, it's nowhere near the limit of the LiIon voltage.

I recently read about new LiIon formulations/packaging technologies that allowed a cell to handle 150,000 cycles. Phenomenal performance. Part of what kills today's cells is oxidation; apparently the vented cell construction allows oxygen to enter the cell which slowly kills the electrodes, and this is why all current cells have a 1-2year lifetime regardless of charge cycles.

None of which has anything to do with NiMH, sorry for the thread hijacking.