Panasonic eneloop AA & AAA Rechargeable Batteries - 4-Pack AA (2100 Cycles) & 8-Pack AAA (2100 Cycles) Ni-MH Pre-Charged Batteries for Cameras, Flashlights, Toys, and Electronics - BK-3MCCA4BA & BK-4MCCA8BA

Update: 6.17.15 - The best just got better, Eneloops can hold up to 70% after 10 years! As indicated on their official website, it's unclear if fully charged Eneloops can hold up to 70% after 10 years or the latest set of Eneloops are able to hold up to 70% after 10 years. It would be impressive if this were true, but after 10 years i think the cycle number would greatly be reduced as testing showed less cycle usage on older cells. Still NiMH technology can be impressive as i have 16 year old cells that work in a clock for a couple of months. It'll be interesting how an aged Eneloop would function.Update 11.04.14 - Be aware of the Chinese knockoffs of Eneloops, they are nowhere near as good as the Japanese ones. The Chinese Eneloops die around 500 cycles while the Japanese ones continue running over 800 cycles. Try to get the Japanese Eneloops if you can as they are generally more reliable. Hopefully Amazon will continue to carry the Japanese ones.Update 9.27.14 - Did a battery test of the pack i used and the battery that was fully discharged still managed to produce the necessary mAh and was slightly higher than the others. For some reason or another only 2 batteries was slightly higher (maximum of 39mAh difference) capacity so it's unclear as to the reason behind that, though 2 of the batteries were numbered and were discharging for a bit in a tv remote and then in a flashlight so it appears that the more often you use them, the more mAh they will produce. That seems to be the case with any NiMH battery, it's best to use them versus leaving them in storage for a long time. So it is highly recommended you buy what you need, if you need some extras or 'in case' make sure you cycle them through and not just leave them sit in storage for several years without using them. Since basic Eneloop batteries have high recharging cycles, it's better to discharge them fully a few times to break the battery in and use them a few times in a high drain device to keep them working. They don't have to be drained fully, 40% discharged (that's 40% charge left in the battery) is the best which will help keep the mAh up and fully discharging them every once in a while to prevent overcharging and voltage depression (or memory effect) which NiMHs are highly resistant that or even don't even have that problem such as the company has stated, they mostly are susceptible to overcharging though which does cause the voltage depression phenomenon which acts like there is a memory effect.Regular, cheap NiMHs or just cheap NiMHs in general lose their mAh capacity over time and even when they are just being used.. avoid those types. Eneloops appear to be the best, AmazonBasics, Duracell and most Energizers are good alternatives if Eneloops are not available but avoid most cheap chargers and find a smart charger with Negative Delta V, overheat protection, and capable of charging any number of batteries. The Panasonic sounds like a pretty good, cheap alternative and get the ones with the batteries as they are a better deal. I plan on getting some Eneloops Pro that comes with one of these chargers but with the basic 2100 cycle Eneloops, it's probably not needed to have the higher capacity ones but they do last a bit longer on a single charge for critical usage. I can't wait to see how long these batteries will hold up during the test of time. Using rechargeable Duracells, they hold their charge for a very long time.. almost 10 years in service and only has a loss of mAh capacity but they still perform for a pretty long time, can still be a few months sitting idle while the Energizers i got around the same time (the 2500mAh ones) lose their charge within a few weeks, but can be recharged and then sit for awhile on the charger and they will get a bit more charge out of them but those will primarily be used in tv remotes and other really low drain devices where i don't mind recharging them every few weeks. Anyway the Eneloops perform well and seem to have a long life ahead of them.==I got the 16 pack and also heard that these batteries are similar to the AmazonBasics which claims they do not lose capacity when over discharged. While i am still in the process of finding out whether the battery that i subjected to an over discharge has lost mAh capacity it held it's ground from zero volts. With the battery fully discharged (or near death) i threw it in a remote with a charged Eneloop and it was showing a sharp decrease from 0.9 volts to 0.4 volts. Then the battery stabilized itself there with no decline or any indication that there was cell reversal (which charges the battery in reverse). I wasn't sure what to make of that, but i have concluded that there is indeed some over discharge protection. I decided to put more strain on the battery and threw the batteries in a flashlight, to my amaze the flashlight, dim as ever was able to light up. I let the batteries sit in there 15 minutes to see if the light would stop working but even after 15 minutes the light was still going. I took the battery out and it was registering just under 0.1 volt. While i was being distracted that i didn't have enough time to unscrew the flashlight to get to the battery i threw the the batteries back in the flashlight and checked it again after 5 minutes. It was still showing just under 0.1 volt. No reverse voltage.It appears that after my test these batteries do not reverse charge and is somewhat resistant to over discharging, which would be fine mixing a pack of these batteries in different devices. Even after my tests i wouldn't recommend mixing the batteries as i am sure even once these batteries reaches 0.7 volts, they start eating up cycles. I have no idea whether keeping the batteries in a discharged state and using them would start reducing the life of the battery or that they would take up a few cycles, but i still need to test the mAh of the batteries to see whether the one i over discharged has lost capacity, which is the other claim from AmazonBasics and i think Eneloop advertises the same thing. It would also make sense why the AmazonBasics has lesser rated recharge cycles then Eneloops. Eneloops do not advertize they can handle over discharging and it makes sense why they don't want to. They want to make sure the consumer gets the most recharges out of their batteries which would make these batteries the number 1 rechargeable battery company of all time.Which is why i highly recommend these batteries. These batteries will last a very long time if you take care of them. You probably will never need to buy new batteries as if you were to charge these batteries daily (or discharge them daily) you would still get about 6 years out of them which is hard to come by with rechargeables that are constantly being discharged and recharged with minimal rest. I'm going to give these batteries another test which will only be 2 AA in 100-130F heat. I have had some people say they don't want to switch to rechargeables because they think that heat will ruin the batteries. I beg to differ, while the batteries might not last as long.. with this other test these batteries should have no problem being able to work in the heat and while it might reduce these batteries life to about 2-4 years, it's far better than replacing the batteries weekly spending more money than what you would on rechargeables.On a fresh charge opened from the package, while it was difficult to understand the date code of the batteries "14-05LJ" and "14-0400" I assume the 14 means the year which would mean these batteries were produced earlier in the year, but again it's not easy to tell based on the letters. If anyone knows that information, leave a comment. Back to a fresh charge from the opened package (literally) I am a bit disappointed from Amazon sending me a product that has been opened, it's possible that it opened during shipping but i did get 2 different date codes on the batteries, but it also appears that Panasonic shipped them this way too. I will say that Panasonics packaging is left to be desired, they could have packaged the 16 pack in a more secure packaging or give consumers a plastic container with the batteries in them but i'm not complaining.. eventually i will put them in a more secure container but for now, the package is holding with some tape.On a fresh charge, these batteries were able to give my phone a 92% charge using a USB charger, powered by AA or AAA batteries. Provided that if i never did charge the batteries i wouldn't have gotten the 92% charge but after recharging the 4 set of batteries i used already, i will see how much of a charge the batteries will put into after a full discharge. I have noticed a few complaints about the batteries not being fully charged and while there are a few different reasons why there is a rare chance that you would get a set of batteries that are discharged or will not recharge correctly. It is a fact of life and happens with any kind of product out there on the market when they are massed produced. It's also rare that businesses would actually strive to lower that percentage because anything with a 1% defect rate is acceptable loss limits when dealing with a world that strives to have profit over making that 1% happy, though many companies do have exchange policies if you received a defective product.A couple of things to think about. These are 1.2 volt batteries and while most devices that require 4 batteries will function fine with 4 NiMH batteries, any higher than that and you would start to see a declining performance or even if your product will function with 6 1.2 volt batteries versus the 1.5 volts. The other thing to consider though with that is alkaline batteries are about 50% charged at 1.2 volts so these devices might run fine even with 1.1 volts but that really depends on the device. Recently, i have found that some devices can ask for more than 1.2 volts and can be considering the NiMH batteries as dying or low but it greatly depends whether the device is detecting the voltage or the mA being produced. With that being said, before assuming that these batteries do not come charged consider these things first that the device may ask for more voltage, your charger is a cheap model or does not function properly, batteries only carry 50% of rated capacity from the manufacture which a refresh is in need or that you require more than 4 batteries and the device will not function properly under the 1.2 volt batteries.With that being said, before you assume these batteries are at fault, try it in a different device or in a flashlight that only requires 1-3AA first after refreshing them a few times and see how they work. With the initial use, i managed to charge my phone up to 92%, it was lower than the http://www.amazon.com/Duracell-Rechargeable-Batteries-Duralock-Technology/dp/B00DSYFAEQ which managed to charge a few devices without being depleted, those are rated at 2400mAh, still on first use these 2000mAh hold up really well and are ideal in just about anything. While there are some devices that won't work well with 1.2 volt batteries and it's not a good idea to use rechargeables in smoke/carbon dioxide detectors or anything really vital to your safety i recommend using http://www.amazon.com/Duracell-Alkaline-Batteries-Preserve-Technology/dp/B00EDK4HXY for high drain devices that often need replacing, for the smoke/carbon dioxide detectors, the classic Duracell battery also rated to last 10 years will work just fine.Other than that, these batteries hold up really well and i will post back when i got more info on the set of 4 batteries i have been testing with and will soon test another set out in my 2D Maglite (using D spacers of course) to see how long they hold up for.