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I decided to splurge on a Duracell brand rapid charger, which, as advertised, will bring cells up to a full charge in a few minutes. It was not a cheap option--on sale I got mine for about USD52 + taxes, but this includes 4 AA 2400 mAh cells, for which I have other uses. But since I am concerned about the waste of disposables the higher frontend cost seems reasonable.
A full charge easily seems to give me quite a few days of very regular use. As someone in the earlier thread pointed out, voltage and capacity, as reported by Edwin Cordoba's BatStatus, drop fairly quickly to about 3.9V and 50% respectively, and seem to hover there for quite awhile. Indeed, I have yet to use the calculator until the low battery icon starts displaying--perhaps I should for the sake of the battery life. The cells take a few minutes to charge in the rapid charger, during which the backup cell seems to do a fine job preserving calculator memory. I have also gotten in the habit of regularly backing up main memory and flags to the SD card, and have a little program that automates the process.
In short, it looks like I can use NiMH cells with the 49G+ and run little risk of losing my work. It seems that rechargeable cells are actually a suitable alternative for the 49G+ and 50G after all, despite official recommendations to the contrary. NiMH seem to do the trick for me, and it looks like that there could be even better alternatives out there, like hybrid cells and rechargeable alkalines and the like.
Les
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Does anybody know if really rapid charging has any bad effects (i.e. shorter lifetime) on the NiMH cells? My charger for these things is quite leisurely (overnight, at least, for a full charge). After a couple of years of fairly light use, my AA batteries are still working well, although I have the feeling that I am beginning to see a shortening of how long they last per charge. They've been through fewer than 30 charge/discharge cycles.
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I don't really know, but from what I've read, slow charging (as with a charger really designed for NiCd cells) is bad for NiMH cells. "Quick" charging (although I don't, offhand, know which rates) is supposed to be better for NiMH cells.
Also, if using a charger that charges 2 cells in series only, and 1 of the cells doesn't need as much charging as the other, then it will be over-charged, resulting in a shorter lifetime. Try to get a charger that charges each cell individually, especially when you're using an odd number of cells in a device, as in a 49g+. The best are supposed to be those that use a "negative Delta-V" method to determine when to switch to a trickle-charge mode or stop charging completely.
I really don't have that much experience with NiMH cells, but so far, the only problem that I've noticed (other than the self-discharge and relatively sharp drop at the end of the discharge curve) is that all of the NiMH AA and AAA cells that I have are slightly larger (longer, larger diameter, and corners not rounded as much) than is typical with ordinary alkaline cells, resulting in a tight fit in some devices.
I haven't tried the "hybrid" (NiMH + alkaline?) cells, but I've read that they're supposed to have a much slower self-discharge rate, but on the other hand, can be recharged maybe only half as many times as more conventional NiMH cells.
Regarding the rechargeable alkaline cells, specifically Rayovac Renewal cells, I was lucky with them (no damaged calculators), but note that they can't be successfully recharged all that many times, and worst of all, my experience was that after being recharged several times, they started leaking while in the charger. I decided not to use them any more.
Regards,
James
Edited: 30 Apr 2007, 2:10 a.m.
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My Duracell quick charger has dedicated "lanes", it seems--indeed, if one loads a fully charged cell into it along with a discharged cell, it will give an error condition (blinking LED) until the full cell is removed. So it seems smart that way.
If the quick charger is a little harder on on NiMH cells vs. a standard charger, so be it. I have no illusions about NiMH cells lasting forever either. But still, from a "green" perpective, I would rather go through a set of NiMH AAA cells in my 49G+ every couple of years than piles of alkalines, even if it really isn't that much cheaper in the long run. Indeed, my spouse and I have tried to make a commitment to using NiMH cells around the house wherever we can in things like electric toothbrushes, TV and VCR remote control units, battery operated clocks, my beard trimmer, the remote mouse on her computer, etc. About the only thing around here that doesn't use NiMH cells are the cordless phones, my older calculators, and the smoke alarms.
The one advantage to all this is that my previously neglected 49G+ is now getting regular use--I feel liberated in using the machine knowing that when the cells run low it is little time and hassle to rejuice the cells. I don't seem to have the keyboard problem on this unit (yet), so I want to give it a good workout and get to know the machine more before I go to the expense of the 50G.
Les
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I had the same question myself, in a general sense. So I searched the web for "NiMH batteries" and got boatloads of hits. Very useful info, though I don't recall exactly which sites I browsed. I use NiMH for nearly everything. My understanding is that the newer batteries decline slower than the older batteries, due to changes in technology. I keep my recharged batteries in the fridge; they hold a charge much longer that way. I use the battery check feature in my 49 and 50 periodically to check the voltage levels so that I am not caught unaware when the battery dies. I have a small plastic case in which I carry 4 cells (now) for the 50. It seems that charger technology is getting smarter and cheaper.
Rich
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Thank you for your interest in Sanyo batteries.
Please do not store your batteries in your refrigerator. The
difference in temperature in your home and the refrigerator
is really not enough of a difference to make it worth
storing them in the refrigerator. Due to safety reasons, we
recommend that you do not store your NiMh cells in your
refrigerator with your food items.
Please let us know if we may be of any further assistance.
Best regards,
SANYO Energy
http://www.sanyobatteries.com
Thank you for your interest in Sanyo batteries.
Please do not store your batteries in your refrigerator. The
difference in temperature in your home and the refrigerator
is really not enough of a difference to make it worth
storing them in the refrigerator. Due to safety reasons, we
recommend that you do not store your NiMh cells in your
refrigerator with your food items.
Please let us know if we may be of any further assistance.
Best regards,
SANYO Energy
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For NiMH cells perhaps the refrigerator doesn't extend the life much, but it definitely does for alkalines.
The concern about contaminating food is exaggerated. Just keep the batteries in a sealed plastic container. It's not likely that they will leak, but if they do, the container will keep them from contaminating anything else.
Do not keep any normal consumer-grade batteries in a freezer. My mother tells me that when she worked in surgery, certain kinds of batteries were kept frozen. Howver, normal batteries are not designed for that, and freezing them may damage them and cause leakage.
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