Originally Posted by
Kingshead
Apparently you didn't read my post or you would have read about my experience with rechargeables in a toy train, it was a disaster, and a waste of a lot of money.
I read your anecdote, but noted that it was totally contrary to my own experience with many different motorized devices, with rehargeables performing far better (and being far cheaper) than alkalines.
The main exception would be poorly designed devices that require voltages higher than 1.4 volts to function -- but even these stop working when the alkalines are slightly discharged. (The other exception would be devices that use very very little current -- TV remotes, for example, where the self-discharge rate becomes dominant.)
The new LED lights use voltage regulation but continually running them with low voltage will shorten it's lifespan.
So, 90,000 hours rather than 100,000 hours? I'll take the risk, but I'd still like to see your citation.
And just what do you think the discharge curve of an alkaline looks like? Do you think it's flat? According to the curves given at
here it looks like alkalines drop off significantly faster than NiMH cells, especially at high discharge rates. If your light really does use 5 watts with AAA batteries (about 1 amp), the discharge curve is likely roughly comparable to a 2 amp rate with AA batteries (the cells are twice the size) -- and it's under 1.0 volts quite quickly. If you're really worried about wearing out your voltage regulator with lower voltages, maybe AAA alkalines aren't the way to go either -- their voltage is only higher for a small portion of their lifetime for high discharges. (Unless you buy the much more expensive "lithium" alkalines, of course -- which do better but cost 2-3x as much.)
I don't want to argue about this but as my life's work has been dedicated to electricity (Electronics Engineer, Master Electrician since 1987, College professor teaching Industrial Electricity, etc) I'll overlook your thinking I don't know what I'm talking about. I'm not going to get into the technical aspects, it's just not that important.
It's never a good sign when somebody has to resort to listing their educational credentials to support their argument -- it tends to indicate that their argument can't stand on it's own.
I'll leave my education out of it, but my life's hobby (R/C planes) has intimately involved batteries (especially once I went with electrics about ten years ago) for nearly as long as your career. And I've had lots of toys and devices that used batteries over the decades. My experience disagrees with yours, including my experience with bicycle lights.
I've most likely worn out more rechargeable handtools than you've ever seen
Ha! The old "I've forgotten more X than you ever knew!" argument.
so I'm no stranger to how they work. Their design takes into account the voltage the supplied batteries output, and the new Lithium Ions drop off rate is outstanding, but the older Ni Cads run longer and have a longer useful lifespan.
If by lifespan you mean how many years until the battery pack has lost most of it's capacity, then maybe.
But beyond that, per unit mass, lithium ion/lithium polymer cells contain significantly more energy than NiCds, and the good modern ones have significantly lower internal resistance. (I've got a LiPo pack right here that's rated up to 70C! It weighs less than one pound, and can put out 2000 watts -- for a little less than a minute.)
If the power tool maker takes advantage of this to put in a smaller battery, that's nice, but it doesn't mean that NiCd is superior to LiPo. Your anecdote doesn't qualify as scientific data.
Try putting a higher voltage rechargeable into your hand drill and see how much faster it runs.
Yes, unloaded motor speed is roughly proportional to voltage. This has little to do with the brightness of lights, however.
But initial voltage is only one part of the discharge curve.
Numbers don't lie, do the math, 20% less voltage is still 20% less voltage no matter how you want to spin it.
But, as I said already, it's *not* 20% less voltage. Try 7%. Alkalines start at 1.5 volts. NiMH starts at 1.4 volts.
And again, at high discharge rates (over 1C), alkalines drop down below 1.0 volts very quickly where NiMH cells do better.
In short, you're largely wrong about rechargeable batteries.