Buying batteries when you already know what brand (Eneloop) and size (AA) and configuration (4 batteries plus charger) that you want would seem to be a straightforward process, but because of the multiple listings/product types here, I spent longer than I had expected to simply comparing the various prices/configurations/product reviews in order to decide which item to purchase.
I ended up choosing this product listing (there were at least 2 or 3 others), and I'm glad I did.
Firstly, there are a lot of reviews of Eneloop on this wider site that mention that chargers have been sent out to UK buyers (by some sellers) which have built-in European plugs which require UK plug adaptors, making the unit bulky and often too heavy for the UK wall socket to hold up. It is not clear which sellers are doing this, but I can report that I ordered this item from the seller iCell in July 2011 and it came with a built-in UK plug, which is what I wanted.
(By the way, you can always email a seller before you buy an item to ask any questions, which I suggest you do if there is any uncertainty about what you will be receiving. I don't think any seller here should be able to sell electronic products that aren't "wired for" the UK market, but if it's happening, and apparently it happens a lot, you can still do what you can to communicate with your seller of choice to make sure that you'll get what you are expecting.)
Secondly, there is a thorough and intelligent review of one of the other similar Eneloop items on this site that says that the new model of charger is being sent out with the old model of battery. He said something about how the old batteries (if unused) stay 85% charged for one year and can be charged around 1000 times, while the new batteries stay 75% charged for three years and can be charged around 1500 times. I didn't go for the item sold on that product listing, and instead went for this item with this product listing (under which there does not seem to be any review that discusses the two battery models), but I wondered if this charger is the old or new model, and if the batteries that come with it are of the old or new model....
In case it helps anyone determine if this model of charger / model of battery is what he/she is looking for, I will describe exactly what I received from iCell today:
Bar code: MQN04-U-3UTGA
Printed on packaging next to a drawing of a 3/4ths full battery: "After 3 years, 75%" and "up to 1500 times"
4 AA Eneloop Batteries: Voltage 1,2 V, Typ. 2000 mAh, Min. 1900 mAh
Because the packaging talks about 75% charge for 3 years, I am assuming that I have received the NEW model of battery. That probably means that I have received the new model of charger as well, but I am not motivated enough to try to find that other review to read about how to figure this out. (I was looking for a basic charger with good batteries at a decent price, so I would have been happy with the old models of the charger and batteries, as long as I got a unit with a built-in UK plug, because I have too many other electrical items that I have to use a UK plug adaptor for, which can be fiddly and a hassle.)
Thirdly: This thing is pretty heavy. Not something I'd take travelling unless I had a definite need for charging batteries on the road.
Fourthly: Although this comes with AA batteries, you can also charge up AAA Eneloop batteries in it. You can buy those separately. I believe I had an Eneloop charger in the US that also charged a third size of battery (the big type of battery that often go in American smoke alarms; I think it's called "D" or maybe "C"), but this one only takes AA and AAA.
Fifthly: The charger will not charge up only 1 battery, nor will it charge up 3 batteries. You must charge either 2 or 4 batteries at one time. There are 4 slots, and you have to fill either the right 2 or the left 2, or all 4. You can't, for example, put 1 battery in the far right slot and 1 in the far left slot. You should not put an AA and an AAA in the 2 slots on the same side of the charger, but the instructions imply that you can charge 2 AAA in the 2 slots on one side and 2 AA in the 2 slots on the other side simultaneously.
Sixthly: The instructions say that Eneloop AA batteries take approximately 10 hours to charge and Eneloop AAA batteries take approximately 8 hours to charge. It says to remove the batteries after you expect that they have charged sufficiently. The little LED light does not tell you if the batteries are charged or not -- it simply tells you that the device is on, and it has an automatic timer to turn itself off after 16 hours, at which point the little light will go off. Therefore, don't look to the little light to tell you if the batteries are charged and ready to be taken out -- that is not what this LED light is for. There is actually nothing on the unit that indicates when the batteries are charged up. It appears that they are not recommending that you routinely leave the batteries in the charger for 16 hours until it turns itself off, just that this is a cut-off mechanism in case you forget about them, kind of like many modern clothes irons which shut off if not moved for a set number of minutes.
Seventhly: It is only meant for Sanyo Ni-MH rechargeable batteries, not ordinary disposable batteries or other manufacturers' rechargeable batteries. (Apparently Sanyo makes other brands of rechargeable batteries, other than the Eneloop brand, and it seems you can use those in this charger. They require different amounts of time to charge up - details of that are in the instructions).
Eighthly: You need to put the batteries in the charger before you plug it into the outlet - don't plug it in and then add the batteries to it. Apparently the shut-off timer will not work if you add additional batteries to the unit after you have begun to charge some batteries, so make sure you have it loaded up the way you want before you plug it in for a charging session, and don't take batteries out or put batteries in while it is plugged in.
Seller ICell sent this lightening-fast to me - I got it by regular post something like 36 hours after I ordered it, even though it had to go from Guernsey to the UK mainland. The package had an import/customs label on it but had not been opened at the border.