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[Note: The following is an updated version for my original “Sanyo eneloop FAQ”, first published in May 2012]

I have been using eneloop low-self-discharge NiMH batteries since beginning of 2007, and I'm completely satisfied with them. One thing I noticed is that newcomers to the rechargeable battery arena often have similar questions/confusions about eneloop. So here is my list of eneloop Frequently Asked Questions. This list is work in progress.

[Q1] Why are there so many eneloop batteries with different capacity ratings and cycle-life numbers?
[A] There are actually three families of eneloop batteries:
- Standard version: The original Sanyo eneloop (circa 2006) was rated for capacity of 2000mAh typical for AA (800mAh for AAA) and 1000-cycle lifespan. Subsequent generations advertise longer lifespan (1500/1800/2100-cycles) at the same capacity. The charge retention rates have steadily extended from "85% after 1 year" to "90% after 1 year; 70% after 5 years"
(Refer to my uploaded photo on how to identify different generations of eneloop cells)
- High-Capacity version: The original Sanyo XX (circa 2010) was rated for 2500mAh but only 500 cycles. The charge-retention rate is slightly poorer at "75% after 1 year". Newer Panasonic eneloop PRO bumped the capacity to 2550mAh and charge-retention rate to "85% after 1 year".
- LITE version: Those have half the capacity of standard eneloop but twice the cycle life. They are not marketed in the US.

[Q2] Do I get better performance from the latest generation Panasonic eneloop cells verses earlier generation Sanyo eneloop cells?
[A] On paper, newer generation offers longer cycle life and lower self-discharge rate. In practice, however, you’ll see no difference since they all have the same capacity. The difference in charge retention rate and cycle life may become noticeable after ~10 year, if at all.

[Q3] Is there any physical difference between PRO and standard version of eneloop cells?
[A] The PRO cells are slightly thicker, with diameter of ~14.4mm (verses ~14.1mm). So they may not fit if your appliance’s battery compartment is too tight-fitting.

[Q4] What is the difference between 'Pre-Charged', 'Hybrid', 'Stay-Charged', 'Active Charged', 'Ready to Use' and 'Ready to Go'?
[A] Those are all marketing terms for Low-Self-Discharge (LSD) NiMH batteries. Sanyo first used the term 'Pre-Charged' for Sanyo eneloop back in 2006. The latest Panasonic eneloop says “Ready to use” on each cell.

[Q5] I see a lot of other brands of rechargeable batteries advertised as Pre-Charged. Are they just as good Panasonic eneloop?
[A] In general, NO. Sanyo/Panasonic eneloop is still the best in terms of charge retention rate and cycle life. Many lesser-known brand also claim to have low self discharge rate and high cycle life just like eneloop. But based on my testing, none actually delivers.

[Q6] What about the AmazonBasics Pre-Charged Rechargeable Batteries?
[A] To clarify, there are three different versions of AmazonBasic rechargeable NiMH batteries:
- The original AmazonBasics AA NiMH Pre-Charged Rechargeable Batteries came in black wrappers. They are made in China and have the capacity rating of 2000mAh. They are NOT as good as Sanyo eneloop batteries.
- The second version of AmazonBasics Pre-Charged Rechargeable Batteries came in white wrappers. They are made in Japan and also have the capacity rating of 2000mAh. They appear to be rebranded 2nd-gen eneloop.
- The third version is also black but called AmazonBasics High-Capacity Pre-Charged Rechargeable Batteries. They appear to be rebranded eneloop PRO. They are rated 2400mAh, but actual capacity is around 2550mAh.

[Q7] How do the Duracell Ion Core pre-charged Batteries compare to eneloop or AmazonBasics cells?
[A] The Duracell 'ion core' AA cells appear to be rebranded eneloop PRO AA cells, while the Duracell AAA cells are most likely rebranded 2nd-gen eneloop AAA.

[Q8] My Panasonic eneloop AA batteries say '1900mAh' on them. Are they counterfeits?
[A] All standard eneloop AA cells (from original to 4th gen) are rated "Typical 2000mAh, Minimum 1900mAh". The confusing part is that 2nd-to 4th-gen eneloop AA cell have "min.1900 mAh" printed on it, even though the actual measured capacity is typically over 2000mAh.
For AAA cells: Standard eneloop are rated "Typ 800mAh, Min 750mAh".

[Q9] How do I find out the manufacture date of my new eneloop cells?
[A] Each eneloop cell has a date code embossed on it. Shine a strong flashlight from the side and slowly rotate the cell to find it. Date codes are in the form of YY-MM. For example, if it says '12-08' that means Aug 2012.

[Q10] Date codes on my new eneloop cells indicate they are made in 2012. Should I return then for newer batteries?
[A] Relax! Unlike ordinary NiMH cells, Sanyo eneloop are still perfectly good even after 10 years in storage. Once you recharge them, they will return to 100% capacity again.

[Q11] I just received some new eneloop batteries. Do I need to recharge them before use?
[A] You can use them right out of the package. However, standard eneloop cells are only charge up to ~75% when they left factory (High-capacity version usually just ~50%), So you can use a Smart charger to 'top-off' their charges. Do NOT do this with a Dumb charger because it will badly over-charge them.

[Q12] I thought I have to drain my batteries completely before recharging them?
[A] This is only necessary if you are using a timer-based dumb charger. With a smart charger, you can top-off your batteries anytime.

[Q13] Can I use other brands of chargers to recharge Sanyo eneloop batteries?
[A] Sanyo eneloop batteries can be recharged using any good-quality Smart charger designed for NiMH cells. But for longer battery lifespan, avoid ultra-fast (15- or 30-minute) chargers and Dumb (overnight) slow chargers

[Q14] What is the difference between 'Smart' and 'Dumb' chargers?
[A] A Smart charger monitors the voltage profile of each cell individually during charging, and stops when a charge-termination signal (negative delta-Voltage) is detected. This is the only way to avoid over-charging. A Dumb charge relies on safety timer to stop charging, or has no termination mechanism at all. This usually results in over-charging which is bad for battery lifespan.

[Q15] How good is the Sanyo MQN06 charger bundled with most older eneloop packages?
[A] The MQN06 is semi-smart but has two issues: it charges in pairs (monitors the combined voltage of two cells), and the charging current is only 300mA. That means it take about 7 hour to recharge a pair of eneloop AA cells. A better choice is the Panasonic BQ-CC17 which charges each cell individually (but still at the same 300mA current)
[Note: Charge time (hour) = Capacity (mAh) / Current (mA) ]

[Q16] What is the best charging speed for eneloop cells?
[A] Choose a charger that gives you charge time between 2-5 hours. That means charging current of 400-1000mA for AA, 200-500mA for AAA..

[Q17] Isn't it true the best charging speed for NiMH and LSD-NiMH battery is the slowest?
[A] That’s only true when using a dumb charger which blindly charges for 12-15 hours, so the current has to be below 0.1C (200mA for a 2000mAh cell) to avoid over-heating. For a smart charger, the current needs to be at least 0.2C to ensure proper termination. If the charging current is too low, the negative delta-V detection may not work reliably. (The BQ-CC17 is an exception since it uses pulsed current)

[Q18] I always keep a set of ordinary NiMH batteries in the charger to keep them freshly charged. So why do I need low-self-discharge batteries?
[A] You don't need to do that with LSD cells. Just charge up a spare set ahead of time and keep them in your drawer. Swap them in whenever needed, just as how you use disposable cells.

[Q19] Why should I buy those 2000mAh eneloop instead of regular NiMH batteries that are rated 2700mAh or higher?
[A] All rechargeable NiMH AA cells rated 2700mAh or higher are susceptible to rapid-self-discharge problem. Beware of off-brand batteries that claim '3000mAh' or higher. Most of them can't even deliver 2000mAh.

[Q20] Can I use eneloop in places with extremely hot or cold weather?
[A] As a rule of thumb, every 10 degree C rise in temperature causes the battery's self-discharge rate to double. So although your eneloop cells can still function correctly, their shelf life will be reduced at high ambient temperature.
For cold weather it is not a problem, since eneloop cells are rated down to -20 degree C.

[Q21] Should I store unused eneloop batteries in the refrigerator to extend their shelf life?
[A] For ordinary NiMH cells, storing them in lower temperature greatly reduces their self-discharge rate so you can get longer shelf life. For eneloop cells it is not worth the trouble, because they can be stored for years at room temperature.

[Q22] Can I use eneloop batteries in cordless phones?
[A] Yes - as long as your phones (such as Panasonic DECT 6.0 cordless phones) are using individual AAA cells, instead of battery packs with special connectors.

[Q23] Do rechargeable batteries only go bad after they meet the number of charging cycles, or their lifespan is limited by time also?
[A] Capacity of a NiMH cell gradually deteriorates with number of discharge cycles. The 'lifespan' claimed by manufacturer is the number of deep-discharge cycles before capacity drops to 50%. This is done under tightly controlled test conditions, so in real life your result may vary.

[Q24] When rechargeable batteries go bad, do they also spill chemicals (like alkaline cells) or just won't hold a charge?
[A] Good-quality NiMH cells do not spill electrolyte as they gradually deteriorate. The only chance this can happen is when they are (a) severely over-charged at a high current, (b) severely over-discharged, or (c) exposed to extreme heat.

[Q25] My baby swing calls for 4 D sized batteries. Do eneloop D spacers work well?
[A] You can use those in a pinch, but expect to replace/recharge your AA cells a lot more frequently than before. This is because the energy stored in an alkaline D cell is about 7-10 times greater than that in eneloop AA cell. See my following review for other options: Panasonic BQ-BS1E4SA Eneloop D Size Spaces

[Q26] My La Crosse BC-700 Battery Charger reports some eneloop batteries as 'null'. Are they defective?
[A] If a battery is over-discharged and its voltage drops below 0.5V, the La Crosse charger cannot detect it and so the display says 'null'. Charge your 'null' battery in a dumb charger for a few minutes, then the La Crosse charger will recognize it.

[Q27] Is the La Crosse BC-700 better than the Panasonic BQ-CC17?
[A] Each has its advantages. The BQ-CC17 is inexpensive, simple to use, and works great for daily charging.
The BC-700 is an Advanced charger. It allows you to determine the true capacity (mAh) of all your batteries, and to revive those under-performing cells. Then you can group cells with similar capacities together for best result. See my "BC-700 FAQ" for details:
http://www.amazon.com/review/RK62EGS3P082I/

[Q28] Panasonic introduced a new charger, the BQ-CC55. Is it worth paying extra over the old BQ-CC17?
[A] Yes, for two main reasons:
(1) Shorter charge time: since its average charging current is 1.4A for 1-2 AA cells, 0.7A for 3-4 cells.
(2) Color-changing LEDs to show the status of each cell: Red=empty, Yellow=half-full, Green=full.
See my review on it for details: https://www.amazon.com/review/R217YKQZZRIRTW/
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TOP 500 REVIEWERon April 18, 2015
The eneloop Pro follows the long-standing eneloop tradition of NiMH batteries that run circles around most of the competition. This eneloop Pro battery is NOT designed for general usage, but rather high-drain applications. When paired with these high-drain applications, the Pro excels in a fashion that few other batteries can, giving you performance that other NiMH rechargeable and disposable alkaline AA batteries cannot provide.
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BACKGROUND & WHAT USAGE THE ENELOOP PRO IS INTENDED FOR
Eneloop is considered by many to be the tour-de-force of rechargeable NiMH cells (much like Panasonic is with lithium ion cells.) Gone are the days where NiMH cells did not give performance that came even close to alkaline. Things like memory, low service lives, rapidly fading capacity, etc. are over. Today we have NiMH cells that can dramatically outperform the finest of disposable alkaline batteries and can be charged thousands of times. Over a 10+ year period, you can save thousands of dollars with a good NiMH setup.

The eneloop Pro is eneloop’s (formally Sanyo and now Panasonic) follow-up to their highly successful eneloop XX series. Like the XX, the eneloop Pro is a SPECIALTY battery. It is NOT intended for usage with lower drain applications, and performs poorly when used for this purpose. However, when used in high-drain applications that tend to be brutal on the battery, the eneloop Pro gives unparalleled runtime that no alkaline can come even close to.
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THE STANDARD ENELOOP 2100 VS THE ENELOOP PRO: Which is right for you?
Eneloop’s newest innovation is 4th generation NiMH cells. Like previous generations, eneloop is offering a standard-use and a high-drain model. These eneloop Pros use 4th gen technology, as do the standard eneloop “2100”. This fourth gen technology gives both batteries a very wide operating temp range, improved stability in output, slower self-discharge, and increases in durability.

Eneloop Pro SPECS:
-Capacity: 2550 mAh
-Service Life: up to 500 recharge cycles
-Rate of self-discharge: about 85% capacity remaining at 1 year of storage

Eneloop 2100 SPECS:
-Capacity: 2000 mAh
-Service Life: up to 2100 recharge cycles
-Rate of self-discharge: Over 70% capacity remaining at 5 years of storage
-A substantial performance improvement with high-drain devices vs. the third gen

THE 2100 --- The standard eneloop 2100 is designed to be a high-capacity battery that is capable of handling all but the worst of high drain devices. This battery makes substantial improvements over the third generation when it comes to handling higher-drain devices. It is ultra-low discharge (literally now it discharges SLOWER than many disposable batteries!) and high capacity at about 2000 mAh. This battery works great in both low drain and high drain apps. Additionally, with a cycle life of 2,100, this battery has serious longevity (literally the service life is four times that of the XX or Pro.) Because of this, most household devices should use this standard eneloop 2100. While it has a lower capacity than the eneloop Pro, the slower self-discharge and the ability to work better with low-drain devices will give better performance than the Pro with most devices. So if you are not using a device in which you constantly have to switch batteries out, the 2100 is what you want. The picture I uploaded shows a basic remote and Logitech wireless mouse; those devices get the best performance from the 2100s because they are not high-drain devices and so I use them exclusively in those devices.

THE PRO --- However, there are some devices that are just plain brutal on batteries. These will benefit greatly from the Pro (or XX) design. For example, in my picture you can see a Fenix LED flashlight and a wireless gaming mouse. These devices put a world of hurt on batteries and run times are measured in hours. The eneloop Pro makes substantial improvements over the already outstanding 2100 in this sort of application. Cameras, audio players, high-output flashlights, medical devices, lasers, etc. will benefit here.

So which battery you need completely depends on your application. I own 4 XXs and 4 Pros to go along with about 20+ 2100s. I use my 2100s for standard applications, and the XX or Pro for high-drain devices.
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WHAT I LIKE
Like eneloops of the past, one thing that makes the brand unique is their advertising. Many battery makers advertise their batteries as having a MUCH higher capacity than they actually do. For example, I purchased 2500 mAh Tenergy batteries and brand new they only had a capacity of about 1700 mAh, and then rapidly shrank from there. I have had similar experiences with both Duracell and Energizer rechargeable cells. Eneloop guarantees each and every battery will meet their minimum mAh rating, and as a general rule all batteries exceed these ratings by a substantial margin. With these Pros, I purchased a 2550 mAh battery and I got a 2550 mAh battery. Additionally, eneloops do not rapidly shrink in capacity like other brands. Fives years or ten years down the line, these batteries will still work great if cared for. This longevity makes eneloop a much better value than inferior NiMH cells: spend a few extra bucks on eneloop today and enjoy their superior performance for years to come while simultaneously saving money.

Eneloop also sends their batteries pre-charged (and they were charged by solar energy.) With the low self-discharge of the Pro, and the extremely low self-discharge of the 2100, you can use these batteries immediately after purchasing them.

While the third generation batteries did a great job with colder temperatures, these 4th generation 2100s and Pros are outstanding. If you want to keep a flashlight in your car, these batteries are hard to beat given they work well in both hot-hot and cold-cold, and temperature extremes will not wreck your service life.
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CONCLUSION: WHAT I LIKE THE MOST
Ultimately, there are two things I like about this battery the most. One, I save a ton of money over disposable batteries. I am talking thousands of dollars while simultaneously supporting environmentally friendly technology. Two, I get better performance from these eneloops and can use my devices longer. As of mid-2015, this is really THE battery to have for your high-drain devices (and the eneloop 2100 is really THE battery to have for your general-use devices.) So I highly recommend the eneloop Pro, as do I recommend the eneloop 2100 and eneloop as a company.

If you are looking for a battery that gives you optimal performance with your high-drain devices, but would prefer an alternative to expensive lithium disposables, the eneloop Pro is the balanced choice of outstanding performance, outstanding value, and outstanding longevity. There really is no substitute.
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on March 14, 2015
Perfect purchase for my Xbox One controllers! I bought eight of the AA cells so there would be extra batteries on hand when needed. My main use for these are for my Xbox One controllers and they last quite a long time. My roommates and I average 20-30 hours of use per week on the controllers and these batteries hold up very well. We only charge them every two to three weeks. Amazing battery life. I also use the AAA cells in remotes and other bluetooth accessories with the same performance level. These batteries last a long time and recharge overnight. Couldn't be happier.

I recommend these batteries especially for Xbox One (or other console) controllers! They perform perfectly at a fraction of the cost for what MS charges for a single play and charge battery pack.
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on October 12, 2017
It's been a little over a month since receiving the Eneloop Pro AA batteries. They've had infrequent use in a transistor radio and have found they don't have as long a use life as the regular Eneloop AA's and need more frequent recharges. That and understanding the recharge cycle is 500 times as opposed to 2100 times for the standard Eneloop battery causes me to doubt the usefulness of these batteries when used in an application that doesn't require high output. My opinion is that they may be useful when high current demand exists, but not for more typical applications. I think in general the standard Eneloop battery provides more bang for the buck.
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Eneloop is a great choice for rechargeable batteries. Compared to disposable alkaline, they save you a lot of money. And compared to "regular" Ni-MH rechargeables, they have superior shelf life (hold their charge while not in use) and number of recharge cycles.

Eneloop has a standard version and this pro version. Which is right for you? The pro version is designed for high-drain devices and have more power. The trade-off is they have a shorter shelf life and number of recharge cycles; the regular eneloop far outperforms the pro for those features.

The tendency is to want the "best", the most power, and go after the pro over the regular. But in truth the regular is the better choice for most applications, and they cost a little less. If your device just burns through batteries, then the pro might be better suited.
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on May 4, 2017
Amazon needs to do a better job minimizing fakes/knock offs products sold. Upon receiving, the package looked worn and didn't look a premium high end eneloop pro batteries shown online. Checked all 8 batteries in La Crosse BC-1000 charger and all had zero charge remaining. Given they're supposed to maintain 85% of their full capacity in a year, zero charge suggests the item is several years old or is defective. Went ahead and did a full charge/refresh cycle on all 8 batteries and none of them reached the 2450mAh minimum capacity. 4 showed full capacity around ~1300mAh. 3 showed full capacity around ~1550mAh and one with the highest capacity at ~1900mAh. If these were cheap no name brand, I would have accepted "you get what you pay for". I purposely avoided marketplace sellers to avoid getting a fake product and paid more hoping it would be genuine. Amazon offered to exchange the item so we'll see if the replacement is a genuine eneloop pro and not another knock off.
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on October 9, 2017
Third pack to have a battery explode and right after my 30day return expired.. What's up with that. Maybe its because I'm in Arizona but everywhere has AC so I don't know if that argument is valid. I ordered 2 packs of 8ct. AAA's and 2 packs of 8ct AA's and all but one of those packs (so far) has had at least 1 battery explode with in the last 30 of purchase! These are supposed to be the best of the best and they have held up pretty good so far now if only they would stop blowing up. Good grief!
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on September 17, 2017
Garbage. Purchased end of Oct 2015, as part of a significant investment in many rechargeable batteries and charger. Bought the "pro" AAA as these were for my LED headlamp. Figured this version would be a better fit for the high output light. From first use, noticed that they would lose charge unusually fast. From a fresh full charge, I'd notice the headlamp would be really nice and bright at the start, but could almost watch it degrade by the minute. Within just an hour or two of use it would be quite dim. This would occur despite using the headlamp on the lower brightness mode. This headlamp was rated at at least 7 hours of use on high power with normal AAA batteries, so something was very wrong. Still, I trusted in their quality and figured this was just the price I was paying for having rechargeable batteries, and accepted that I'd have to charge them fairly frequently. Coming up on two years later now, they are pretty much unusable. I have recharged them maybe a few dozen times at most, total. Well below the advertised "500" for the "Pro" version. Now when I looked closely at them I could barely make out "14/11" on one of them (mostly worn off). So I know they were made in Nov., 2014. That means when I bought them "new" they were already nearly a year old. As of today (Sept, 2017), they're almost three years old. Still, they should have some life left, but are basically garbage at this point, being usable for merely minutes on a fresh charge. I don't know if I got bad ones, or old stock, or some kind of repackaged used stock, but as someone that takes the time to do research and generally spends more to buy higher quality products with the hopes that they will last and be better than cheap version, I'm left highly disappointed by these. Meanwhile all of the non-Pro (white) AA that I got at the same time seem to be mostly fine. I will perhaps go with a different brand in the future, at least for AAA.
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on December 27, 2016
If you're a professional photographer and you're wasting money on one-and-done batteries, you are being foolish. The eneloop PRO AA has been insanely valuable for my speedlites. They last a long time on each charge and provide all the power I need to work quickly. HIGHLY RECOMMENDED for photographers with speedlites. After shooting 3 or 4 events I have made my money back on these.

Sidenote... most things will require less out of a AA battery, so I should mention these batteries are above average and amazing for anything requiring AA batteries. Buying one-and-done batteries is a thing of the past and a waste of money.
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on June 12, 2016
I love these rechargeable batteries. I already have the charger for this with AA batteries and these fit right in there since they have AAA and AA slots. I have been trying to convert all my battery powered electronics to rechargeable or alternative solutions and these are great to have.

They don't take very long to charge at all, I would say about 5 hours max. They last about as long as normal AAA batteries or even longer I would say. I have had zero issues at all with them holding a charge and they always seem to be supplying the right amount of power (1.5v)

The only concern which I haven't tested yet is the battery life time. It claims up to 500 times with the Pro version which I have and then 2100 times with the normal ones. 500 times seems kinda low to me but this is a compromise to the 85% charge hold to up one year compared to the normal ones which is 70%. I will have to keep doing further testing on this and I will update as I go on.

Pros
- Rechargeable
- Can use the same changer as the AA ones
- Holds as long or longer then normal AAA batteries
- Fast charging

Cons
- None
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