Interview with Eneloop Technicians

About 50 questions I had prepared to ask


After an invitation I received from Panasonic, I (ChibiM) met with a group of Panasonic employees on July 13, 2018 at the Panasonic office in Brussels. We discussed many things about Eneloop batteries, chargers and technology. Among the employees were 2 Japanese workers who had been involved in the research and invention of the Eneloop battery from the start. One of them was visiting from Japan, and therefore they tried to arrange the meeting while he was still available.

They were very open, and tried to answer all the questions I had. I can’t remember exactly, but that meeting took about 2-3 hours. They also explained the research they were involved with, before 2005, to see what people were most interested in seeing improved in batteries.

After the meeting I typed these answers out and sent them to the Belgium Panasonic employee who was there during the meeting, to double check for errors. I received them back, and posted them here.

Just to be clear, I don’t count myself as a battery technician, but more as a vivid Eneloop librarian :–)

1.    Did you create the technology or stumble upon it?

Sanyo employees started doing surveys back in 2003 to learn what people didn’t like about batteries, and they found out that most of the interviewees in Japan weren’t happy with rechargeable batteries. Losing charge quickly and not be able to tell whether a battery is still full and usable were the 2 main complaints. The answer to the fast discharge problem was already found within 1 year. And in November 2005 they announced Eneloop.

2.    Why did you use the crown symbol on the first eneloops?

It was a designers idea, but it came from the idea that the Eneloop is the king of batteries.

3.    What’s the real difference between the various generations? Is it manufacturing process, quality control, ingredients? If the same, was it just a discovery that they were actually more than originally thought and highered the cycle number?

The process of manufacturing and the Raw materials were improved overtime.

4.    What is the differences from a technical and design/construction of regular Eneloops and Eneloop Pros that allow the regular Eneloops to retain charge for longer and have more recharge cycles and the Pros to have a higher capacity?

More volume is more capacity. The Pro batteries have a thinner canisters so there is more active material and electrolyte . The reason why there is a difference in the cycle life is the difference between the amount of the positive and negative electrode. The bigger the difference the more cycles it can have. With Eneloop Lite being on the exact opposite of the Eneloop Pro.

5.  What’s the difference between the ones that are made in China vs the ones that are made in Japan? Why doesnt Panasonic produce the same quality in China as they do in Japan?

The quality of the Chinese eneloops are improving especially since 2016. The main difference between them are the production machines. The machines used in Japan were the result of a very high investment to get the best possible machines.. 

6.  Why no real C or D size batteries (and have AA’s inside)? Why are current C+D not sold overseas?

In the Alkaline market AA and AAA have about about 95% of the overall volume and about 5% for C or D size batteries. In the NiMH market AA and AAA’s share about 98% of the market. So there isn’t enough benefit from making an investment into new machinery for such a very minor market.

7.  “Don’t use in airtight devices” some manuals say, what is the worst that ever happened that you know of?

Answered by Belgium employee:If they are severely discharged they will vent a bit of gass due to the chemical reaction, and in case of an airtight devices, this could build up pressure.

8.  Why do eneloop Pro decrease in quality so quickly? In real life only 100 cycles or 2-3 years of use. Is it built up internal resistance?

Yes, they build up internal resistance. And therefore can’t provide enough energy. The size of the positive electrode and negative electrode has to do with this. Positive has to do with Capacity, and the Negative has to do with Cycle life. The closer these numbers match the shorter the lifespan. 

Added info by Panasonic employee Brussels in email: The ratio Between Positive and negative electrode will define the capacity. This means for example there is in an lite an equal amount of negative and positive electrode, however in a pro there is more Positive material ( which will cause a higher capacity) but a far higher amount of negative electrode. So the ratio difference of -and+ will be higher at a at pro then with Eneloop lite. You need more negative material in order to get the high capacity out of the Eneloop pro. But in contradiction to that higher – vs + ratio, the more stress there will come on the battery during charging and the higher the capacity loss will be after several cycles.

9.  Why are there no new (limited edition) eneloops sold in Japan anymore since 2015?

10.               How prone are Eneloops to internal cell damage because of physical shock and vibration (for example dropping them on a concrete floor from a height)?

They aren’t that easily damaged, so a drop from a meter wouldn’t be too troublesome. Added info through e-mail: ( the meter test is also part of internal testing and should not give a problem).

11.               Are Panasonic 2700 also made in the same factory?


12.               How many NiMH factories are there in Japan?


13.               If the battery product code says: 16 06 LM what does that mean? (year/month/?? or year/week/??)

Yes, Year, Month. last 2 codes are for production lines in combination with some other data, in order to track batches of batteries for quality control purposes for example.

Charging / discharging / cycle life

14.    I have 2006 AA Eneloops that still have most of their capacity, even at reasonably high discharge (2 amps). Their internal resistance is higher than new cells, but still pretty good. What is the expected life-span of Eneloops, if cycle counts are not a factor (i.e., less than 100 cycles)?

That is a hard question. They know it wouldn’t be a problem for 10-15 years, but longer than 15 years only time will tell.

15.    What would be the best settings  Panasonic could recommend for charging AA and AAA with a MC3000? Especially refresh, max voltage, min voltage, max temperature, -dV/dt  (negative delta Voltage)?

There is no perfect setting. How more conservative you set the limits how more cycles you’ll be able to get. But generally speaking you would set the Minimum Voltage to 0.9 or even 1V, the maximum Voltage isn’t too important, and could be about 1.6Volts. The charge usually cuts off before it reaches that Voltage anyway. Temperature wise it is best to keep them as cool as possible, but reaching 40-50 degrees Celsius isn’t a problem. At 60 degrees Celsius you’ll be able to start noticing reduction in cycle life. So if you can keep them at 30 degrees, that would be a sweet spot.

16.    What is the relation between deep discharging (< 0.9 Volt) versus cycle life and internal resistance? how deeper how higher resistance? 1 time deep discharge is forever damage to battery? reduced cycle life by X %? If eneloop PRO is discharged below 0.6 of 0.9V would cycle life be reduced with 100 cycles?

The difference between discharging to 0.8V and 0.9V will only be a minimal difference in cycle life. And yes, how deeper the discharge the faster the internal resistance rises. There is no real testing data to prove this point of how much % cycle life at certain voltage is lost etc. but a deep discharge will reduce the cycle life, this can be by 1%, but can be more as well.

17.    What is the fastest way to kill an Eneloop (so we know what not to do)?

Over-discharge is much worse than over-charge!

18.    What are the best charge/discharge levels discharge to 30% and charge to 99%? Do you have graphs of these tests that you can share? Also for longest cycle life, deeper cycles at higher rate, 5000 cycles at 20-80, but more Amps. How to maximize/optimize for cycle life and calendar life (age).

This is almost the same questions. The more conservative you are with the limites the more cycles you’ll be able to get. Also this hasn’t been tested, or at least is the data not shared. But generally speaking between 20-80% would have much more cycle life than 0-100%, possibly even by 50%.

19.    If 0.5 to 1C is recommended, which of the 2 would actually be better/preferred?

The preferred charge rate would be 0.5C

20.    What is worse, charging to 100% or discharging to 0% (overdischarge vs overcharge)

Overdischarge is way worse.. overcharging isn’t as bad.

21.    What is the real MAX Voltage without damage? Whats the real MAX temperature without damage during discharge (any difference between heat during charge/discharge)?

Max temperature is hard to say.. every temperature increase will have some effect on cycle life. See the answer about “best setting”.

22.    Do you have graph of the effect of a periodic refresh V break_in V control (regular recharge without refresh or break_in) of Eneloops?

No, they don’t. They don’t even recommend doing a Break-in, but this is all up to the users. It probably only helps reviving capacity with a very small amount.

23.  There are various alleged algorithms floating around for periodic “refresh”; “break_in”; or “deep discharge”. For example The SkyRC MC-3000, by default, has parameter values for the refresh operation as follows:
Charge 0.5C rest 0.5hours discharge 0.25C rest 1 hours, charge 0.5C (Refresh)
Break in: 0.1C 16 hours rest 1 hour, discharge 0.2C till 1V, rest 1 hours, charge 0.1C  If there is any benefit from these could we get some authoritative definition of the different algorithms from Panasonic .

No, they don’t recommend these refreshes, break ins etc. But yes, they could see some people would gain a few % of capacity.

24.  For eneloops that spend most of their life shallowly cycling around the same (high) SOC (e.g. trickle-charged in a solar keyboard), what is the best way to extend their life, e.g. should they occasionally be given deeper cycles by covering the solar panels?

You don’t need to do a deeper cycle, but that is from common knowledge without test data..

25.  Do you know any good methods for eneloops of estimating SOC from resting voltage or simple (pulsed) load tests?

No, that is impossible! Because the voltage is really stable. You can probably differentiate a 90% from a 100%, but you can’t have any useful info between 20 and 80%.

26.  What is the exact SOC when eneloops are being shipped? 70% ,since when? Jp vs overseas market.

100% in Japan, and 70-75% worldwide. The actually charge the batteries first, and then discharge to 70% for extra long resting/shelf life.

27.  Why does Panasonic not remove the dumb “basic” chargers from the market and sell only smart chargers? if the environment is so important.

This is mainly for people moving away from Alkaline batteries and start using rechargeable batteries because these types of chargers are cheaper.

28.  Is there a way to recover from a extremely high internal resistance? When batteries age.

No, there is no way, except for opening up the battery and replacing the internals.

29.  How long is the life expectancy of an Eneloop cell if it’s only cycled every two years (i.e. if a charge lasts 2 years)?

This is not tested, so they don’t know.

30.  What charger do you personally use?


31.  Why is it BQ CC55 is is almost 0mV but it heats up older non-eneloops very hot.

They would have to investigate. 

32.  I know you recommend -dV/dt charge termination, but is there another way you could terminate charge that is better, (but may be much more costly to produce a charger for?) I heard about the inflection/inflexion point method.

It sounds to me (ChibiM) the BQ-CC55 is using the inflexion point method, it would charge up to 99% of the peak and then terminates by measuring the increase in Voltage every X seconds.

33.  Once a battery is inserted in a device the wrong way around, and shorts, and gets really hot, how do you know if its damaged…

With an alkaline it is easy when it leaked it is damaged, with an Eneloop it will also be a bad sign when the battery starts leaking, however, it is likely that it could still work. So the best way is to charge and discharge an see how much resting capacity is inside.

34.  Stated that their own old line of chargers (basically pre-2013) were designed for Evoltas specifically and are “not compatible” with Eneloops (of any generation).what has Panasonic changed in the newer chargers’ firmware programming to allow cross compatibility between two different product lines?Answered by Panasonic employee in Brussels, through email:
I actually do not know what changes were made in the chargers after 2013. There were definitely changes within charging firmware, in order to align with Eneloop technology, but also there are some liability and warranty issues involved in this.

35.  it seems the newer Panasonic chargers also have a significantly different pulsing current profile than the Sanyo ones did (different voltage and amperage). If this question cannot be answered due to “trade secret” reasons, then: Why are the old chargers incompatible with their counterpart products?

This is very possible to be for warranty/liability purposes only…

36.  Does trickle charge damage regular eneloops? lite and pro?

Trickle charge doesn’t by itself, but continuous charge does.

37.  Eneloop Lite question: Why are the life cycle ratings different between the export version (3000 cycles) and the domestic version (5000 cycles)

Comparison other batteries, innovations, other questions etc

38.    What is the best way to store Eneloops for extremely long shelf-life (i.e., when not used in devices)? What charge level? 40%?

Best in a cool environment, around the temperature of a fridge. And at about 20-30% charge. Best is to first charge to 50% and then little discharge.. Don’t charge up to 40% and stop, because somehow the little discharge helps the battery to keep their charge for much longer. This is a well known behavior, but not clear why this happens.

39.    What new research is being done on making better batteries? What will the next generation be like? Will the new AA standard (same quality) ever be more than 1900mAh?

There isn’t anything new on the horizon, but they try to find a way to minimize the drop from 100% to 90%. The fastest discharge happens between a fully charged battery and about 90%. They would like to figure out to get rid of this quick drop, and have even better LSD capabilities.

40.    How is the NiMH industry doing at this moment? Lithium is growing like crazy. NiMH is getting less?

Alkaline batteries are still widely used so there is still room for growth.

41.    If innovations from EV battery breakthroughs are impacting consumer reusable batteries

42.    Why are eneloops so hard to find on the shelf of stores in u.s

43.    Are Duracell, Ikea same quality/production line as eneloop? whats the difference?

44.    What do technicians do every day? What’s the craziest test you have done/seen with eneloops.

45.    Is the eneloop technology also used for other things other than rechargeable consumer batteries

46.    Could you apply the technology to NiZn batteries? (nickle zinc)

No, they use totally different ïngredients” and are very unstable.

47.  Any solar panel charger for eneloops that will be available worldwide.

For now nothing is really planned, however we are looking into opportunities to expand the Eneloop world.

48.  Sanyo/Panasonic going to make more good USB PowerBanks powered with 2x or 4x AA eneloops? With a 1A current output or more. And rechargeable with USB of course (USB in and out)

49.  Or a battery gauge thing like Duracell used to have where you put your fingers on 2 spots and it would indicate how much juice is left within it.

Added in email: Altough marketing wise the Duracell battery Gauge is very nice to see and use, it is not always a very accurate tool to show th amount of energy left within the battery and due to difference in discharge awy of an NiMH and alkaline not really possible within a rechargeable battery

50.  Would you ever think about a built-in boost driver?

51.  Has Eneloop considered making a USB battery charging port version? (funny micro USB charge port on the side)

Eneloop batteries are one of the best rechargeable batteries in the world.
You can buy them in the following countries:

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