Bests & Worsts Reviews from Amazon

[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/