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I have been using Nuon rechargeable NiMH batteries for about a year now. I use AA, AAA, and 9V, and I have bought the batteries and chargers from Batteries and Bulbs. Now that I have some credibility from long-term, heavy use of these batteries, I want to give my own thoughts on this product and NiMH batteries in general. (To date) I am not a paid advertiser for Nuon and I have never received any free materials.
I'm just going to give my general perspectives, and not bother with references or the hard numbers on cost effectiveness, mA-hours, and such like. You should be able to find that information on the Internet without much difficulty.
The short version is that I think NiMH batteries are a great practical option for typical residential use cases. However, I have to give some caveats regarding voltage levels and cost-savings expectations. It is also important to have a good understanding of how battery refresh works for NiMH batteries.
Obviously this is the main appeal of rechargeable batteries, and you'll need to do your own cost calculations based on the prices in your area, and your own battery usage habits. But roughly speaking, I believe NiMH batteries are generally around 4 times more expensive than non-rechargeable Alkaline batteries, depending of course on how big a pack of batteries you buy. Batteries and Bulbs sells a Nuon charger that handles both AA and AAA batteries, with up to four batteries at a time. This charger is about the same cost as ten batteries, but it does include a pack of 4 batteries with the kit. You need to buy a separate charger if you want to do 9V. If you have kids, and cycle through several birthdays each year, then I would guess you will recoup your initial investment within one to two years.
So you don't get burned by disappointment from false expectations, I think it is important to discuss battery usage habits in families that have multiple children. Maybe you are thinking, "great, I'll buy a charger and a dozen batteries, and never have to buy batteries again". However, remember that your typical American family will use batteries something like this: A Christmas/birthday will come around, you'll by a bunch of batteries to fill up a half-dozen new toys, and then a week later all those batteries will be dead. But then, because you are too cheap or too busy to buy more batteries, those toys/batteries will just remain dead and never be used again. Then you'll just buy batteries for the new toys that come along at the next Christmas/birthday event.
However, what tends to happen with rechargeable batteries is that, since it is easy/convenient to recharge them, the old toys keep working, and remain filled with batteries. So when the next Christmas/birthday comes around, you don't have any spare batteries at hand, and you need to buy some more rechargeable batteries to put in the new toys. So, that can offset the cost savings, compared to the cost of your old habits. So, if you want to save money long term, you'll need to get in the habit at least once or twice a year of going through the toy box, finding the toys nobody plays with any more, and reclaiming those batteries.
For me, this is the greatest thing about rechargeable batteries: I never have to worry about inadvertently draining a set of batteries. If your kid leaves the ON switch turned on for two days, or your calculator doesn't have an auto-shutoff option, it isn't a problem. Just take the batteries out and throw them in the charger. No need to scold anybody or to get upset or to stay worried about whether or not you turned off device XYZ.
Personally, I've never had one of my NiMH batteries leak under any circumstances, whereas I've seen Alkine batteries start leaking after I had installed them just a few weeks before. I've read that NiMH batteries can leak under some circumstances, but it has never happened to me yet.
A trade off with NiMH vs Alkaline, is that NiMH does not charge to quite as a high a voltage for a given battery size. The Nuon AA batteries are listed as charging to 1.2 V, though in my personal experience I usually see around 1.39 volts. Alkalines are generally expected to provide an initial voltage of 1.5 to 1.6 volts. However, this is not an issue with most devices, because most electronics that take AA/AAA batteries are designed to run at a significantly lower voltage than the maximum possible, based on the assumption that the Alkaline battery will lose a lot of voltage as it discharges. Though I'm sure there must be some exceptions, personally I have never come across any electronic devices that couldn't use NiMH batteries instead of Alkaline, including flashlights, calculators, electronic keyboards, and a host of tiny toys too numerous to list.
It is important to understand that, with NiMH batteries, they provide better capacity if you drain them fully before using them again. It doesn't hurt them to do a partial discharge, but they won't provide as much capacity until at some point you drain them fully. The cycle of draining them fully and then charging them again is a battery "refresh". The Nuon battery chargers normally do a "quick charge" intended to get your battery up to max voltage within an hour. However, there is a refresh button on the side which will force the battery through a refresh cycle. The only downside to doing a refresh cycle is that it can take several hours longer, depending on how much charge is left. If you do a quick charge instead, the charger can also somehow detect that a battery needs to be refreshed, and the icon for that battery will blink to let you know. Personally, since I am rarely in a hurry to get the batteries back, I always press the refresh button as soon as I put the batteries in.
I'm not going to pretend to be an expert at Lithium batteries, but personally there are two things I don't like about Lithium batteries: (1) they tend to be more expensive than NiMH, and (2) you have to be a lot more careful about how your charge and discharge them, in order to avoid deteriorating the battery capacity. The primary advantage of Lithium batteries is the higher capacity, but honestly that doesn't make much difference in typical residential use cases, like toys and calculators. It might be something to consider if you need batteries for remote field work, like carrying a small camera into the Amazon jungle for a week, but for most residential applications the NiMH battery capacity is plenty.
From what I've read and heard, my understanding is that NiMH batteries are also considerably safer than Lithium-Ion, and that is another reason I would prefer to use NiMH rather than Lithium-Ion around the house. Of course, some devices come with internal Lithium-Ion batteries and so in those cases I don't have a choice.
Good observations. I've been using a few of these myself. I have found that the Duracell brand does not seem to hold up as well as the Nuon brand. I will say, though, that the rechargeable batteries do not seem to last as long as a non-rechargeable one. But your mileage may vary.
Nuon AA batteries are 2500 mAh. I believe this is about the same as a typical economy Alkaline AA battery, though I've read that some of the fancy ones like Energizer "Max" claim 3000 mAh. I think for your experience, however, the two big questions coming to my mind are (1) were the batteries in need of a refresh, and (2) does the device drop out at a particular voltage level?
Also, to add something to what I mentioned earlier: I've found that all of my calculators operate with NiMH batteries installed, but I've noticed that some of them will lose some LCD screen contrast if the battery is not fully charged. I suspect this is due to voltage levels.
Anyway, one can certainly see how it might be possible to get some extra time out of certain Alkaline brands installed in certain devices, and how that would be a factor in some use cases. But that is not something that matters in most residential use cases; e.g., it doesn't really matter if the toy keyboard lasts 12 hours or 15 hours, if it is easy to throw the batteries in the charger.