Review, Teardown: Sanyo Eneloop Batteries & Charger NC-MQN04A

When Sanyo introduced the Eneloop, it was a revolution in rechargeable Ni-MH batteries. Prior to the eneloop, Ni-MH batteries either had limited capacity (1600-1800mAh) and decent self discharge characteristics, or they had great capacity (2500-2700mAh) and terrible self discharge characteristics. You could charge the batteries prior to use, only to find them completely dead within a week!

The eneloops utilized better separators which enabled the batteries to have low-self-discharge. This reduces self-discharge to the point where storage of charged batteries for a year (and later five years) became a feasible option (with 70% or so of capacity remaining afterwards). This came at a slight cost to capacity (2000mAh for regular eneloops, finally 2500mAh for Eneloop Pro/XX but with charge cycle limitation to 500 cycles), but no cost to charge cycles (initially 1000, increased to 1500, then 1800 and beyond). Wikipedia’s article has a very good run-down of just what the generations are.

No longer were Ni-MH cells non-usable for stand-by operation in many appliances. Low temperature performance was improved as well, and best of all, it ended up costing almost the same as quality Ni-MH cells. There really wasn’t any reason to buy any other cells, even today.

My Eneloop Cells

Eneloop Cells

The eneloop cells in my possession at the moment are (from left to right) the first generation HR-3UTG, the second generation HR-3UTGA, the third generation HR-3UTGB and the XX (or Eneloop Pro) HR-3UWX. You will note that the top of the first generation differs, whereas the second and third generation are very similar. The third generation has the TM marking on the front. The Eneloop Pro is completely different.

Eneloop Cell Markings

Looking at the markings on the cells, the model number is clearly visible, with the second generation featuring a crown and the third features a “doubled” crown. Near each of the seals, a batch code is printed with the year of manufacture. My first generation is dated 2006, second generation dated 2011, third generation dated 2013 and XX dated 2011.

Eneloop Special Editions

The eneloop cells are also available in specially coloured special edition packs, which do not differ electrically from the regular eneloop cells. Sometimes, bargains can be had on such 8-packs, which makes them a tempting purchase.

Eneloop Special Edition Rear

While the colouration may not appeal to all, there is one special feature of these cells which I like – they are number coded right next to the Sanyo logo which makes organizing sets of cells easy. Buy two packs, and you’ll have four sets of four cells with the same number/colour making organizing them a pinch!

Other eneloops available (but not locally) are the eneloop lite series with reduced capacity and price, intended for use in non-demanding situations. Unfortunately with the given price differential, I’ve got to say that it’s not really that appealing in comparison.

All of these cells are made in Japan, and Sanyo is a known quality brand of battery. I was not aware until recently that Sanyo’s battery division was acquired by Panasonic and in future, the eneloops will be under Panasonic branding instead.

I have used these cells with my flash units, point and shoot cameras, and wireless monitors. They perform flawlessly, and they can even handle fast charging. I have no complaints at all. I can’t say the same about the Varta Ready2go series of cells as they seem to be of inferior build and losing capacity much quicker in my experience.

The Eneloop Charger NC-MQN04A

Eneloop Charger

The key to battery longevity and user satisfaction in terms of Ni-MH cells is the charger itself. The eneloop cells can often be had in bundles of four AA cells with a charger like the one shown above, coded NC-MQN04A, at nearly no additional cost. Sometimes such bundles work out to be cheaper than the regular cells alone!

It’s a bit interesting to take a look at the charger itself – we know the cells are great, but what about the charger?

Eneloop Charger RearThe charger itself plugs into the wall directly, and is rated 5W. It’s only suitable for use with 240v AC according to the printing.

The output is two banks of pairs of cells – this means that mismatched cells will see overcharging of one cell which may shorten its lifetime. Further to this, charging of single cells is not possible.

The charger itself outputs 250mA for AA and 120mA for AAA, which stated regular charge times of about 10h for Eneloop AA’s and 8h for Eneloop AAA’s. This is a fairly long charge time, and doesn’t improve the user experience. Further to this, Sanyo thinks it “really doesn’t matter” when you can charge cells beforehand, but in a pinch, a fast charger is always more convenient when there are a lot of cells to be charged!

The supplied leaflet also lets us know that the charger is a safety timed charger with a cut-off at 16 hours approximately. There is no other charge termination provided at all.

I suppose given that the charger essentially costs nothing, one cannot expect to see more advanced features like fast charging, negative delta V charge termination and thermal trip. The lack of these features may adversely affect the lifetime of the cells if frequent overcharging (i.e. non-depleted batteries are charged for the full suggested time, let to get too warm, or left several times to reach the safety cut-off time) occurs.

I suppose it would be nice to know what’s inside. Removing the four screws (removed in the above image), allows the rear half to separate from the front half.

Eneloop Charger Inside

The charger is a strictly “linear” sort as opposed to a switching sort. The primary side of the JEC 21-2447-T1 transformer is directly soldered to the power pins. It may have a fuse wound into the primary winding.

Eneloop Charger Main PCB Rear

The charger is made from a single layer PCB with a single IC – a HEF4541BT timer, which probably is used to perform the safety timer feature.

An analysis of the PCB (along with the other side shown later on) shows that the “charging channel” consists of one half of a centre-tapped transformer winding rectified through a power diode (D2, D3) and passed through a current limiting resistor (R6, R6A, R6B & R8, R8A, R8B) and controlled by a transistor for switch off (Q1 and Q2). Insertion of an AAA cell increases the resistance in series by the addition of R20, R20A, R5, R5A, R21, R21A, R13, R13A.

A second single winding is used with D4 and D5 and a scattering of components to power the timer chip from what I can see. It seems a bit complicated, and Z1 may be used for voltage regulation (at a glance).

Eneloop Charger PCB Top

Two small electrolytic capacitors are present, with a polyester orange dipped capacitor for the timer. The two LEDs are present to indicate charging channel activation. The silkscreen printing of FUSE:125 degrees C seems to allude to a fuse which is not present on the PCB. The PCB itself is a paper type substrate with what appears to be a product code of GW108. This alludes to a manufacturer named GW (Great Wall?). It also has codes 0412-214-28601 E156176 printed.

The charger PCB and transformers are held in by a push fit – no screws are used internally in the charger.


It seems to be a simple construction, but it’s not a really good charger. In some senses, it feels a little bit simple for the quality Japanese cells it comes with. It’s almost wrong to subject those cells to such “rough” treatment. I suppose you could use it if you don’t have anything better, but don’t buy it looking for a quality charger!

About lui_gough

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4 Responses to Review, Teardown: Sanyo Eneloop Batteries & Charger NC-MQN04A

  1. Sandeep Jadhao says:

    I have eneloop cell charger as shown above with transformer jec 21-2377-t1. My cell charger is not working now and transformer is not working according to me and I don’t know the voltage rating for the transformer, so can you please give me the voltage rating so that I could buy substitute transformer from market and make the charger working again. my email id is .

  2. lui_gough says:

    The slight difference in transformer markings may be due to different input voltage. My measurements are (RMS AC) 16.8v between yellow, and 4v between red and black. This means this is a dual-coil transformer with a 0-16v winding and a 4-0-4v winding.

  3. Benjamin E. says:

    I have the NC-MQN06U charger. It’s similar, but better in a number of aspects.
    1. It has a rating of 100-240V, 50-60Hz, 8W for the power input.
    2. Provides 1.2V x2 or x4 (just like yours, this one, charges the batteries in pairs), at 300mA for AA’s, and 150mA for AAA’s. Sensing of which batteries are installed is done by the battery contact switches, which aren’t included in your model of charger.
    3. It uses an SMPS (as obvious, due to the “universal” input range).
    4. Capacitors are cheap/crap – they are “Micon” branded. 2x 4.7uF 400V on the input, and 1x 1000uF 10V on the output.
    5. It uses a 1A 250V ceramic fuse (yay! :D) on the AC input.
    6. Plenty of input-output isolation is provided, with PCB slots and plastic barriers (which are part of the molded enclosure) to increase distance.
    7. The SMPS is regulated (or appears to be), since it features an optocoupler for feedback. The TO-126 transistor (no heatsink attached) is a 13003, and the SMD one – in a SOT23 package – is marked Y4.
    8. The SMPS does appear to use the self oscillating type of design, as I see no ICs for it, other than the typical TL431AC.
    9. Rectifier diodes are 4x 1N4007 on the AC input, and an SB260 on the output.
    10. The AC input is also protected by an MOV, which is a nice touch.
    11. The power input also has a filtering inductor, of the regular single-winding type. It’s forming a Pi filter with the two 4.7uF 400V capacitors. Perhaps this might be to reduce noise, or increase PF – I don’t know for sure.
    12. The charge status indicator LEDs are the rare rectangular type. They are just regular green LEDs.
    13. The batteries are charged with some 14 pin SOIC chip – I can’t read the label, it’s poorly engraved/etched. The chip appears to monitor charging current, each series pair of batteries has two paralleled 1/2W resistors. One is 7.5 ohms, the other is 6.8 ohms, giving 3.57 ohms for each battery pair.
    Interestingly, there are two high-side transistors (SMD SOT23, marked Y4) – one for each battery pair – and ONE low-side transistor (SMD SOT23, marked WB0S). It is connected to the negative ends of both battery pairs, as if to interrupt the current through both pairs simultaneously. I’m not sure why this configuration is needed/implemented, as it appears that the low-side transistor is redundant! Perhaps it cuts off the batteries almost completely, to minimize battery drain from the voltage sensing circuits in the control chip.
    14. Soldering quality is very much superior to your model you dissected – the solder is very shiny, and has no dodgy/poor looking joints. Hell, it’s even much better looking than in many other good makes of power supplies and electronics!!!

    This charger does have an annoying tendency to beep when it has finished charging. And no, it doesn’t have a speaker or buzzer! It’s the SMPS which either goes unstable, or “hiccups” because of the light load.

    One pitfall I see with this charger is that it has that dreaded melamine glue – that brown/tan glue that holds components down, which can degrade over time and become conductive.

    Another pitfall is the label on the back – like your unit, the text is formed with the plastic enclosure itself – making it difficult to read (you have to hold it at a certain angle. I know, it’s not hard to do that, but it gives the user a sense that it is a bit cheap, since they skimped on printing a label (if most users even notice, that is… lol)).

    I’ve had this charger for at least two years, and it’s been working well the whole time.

    The enclosure says the Lot number is 3011I, which I guess is from 2011? I’m not 100% sure … either way, the electrolytic caps don’t have date codes because they are cheapo caps. I probably should replace them for some extra peace of mind, but the charger doesn’t get very warm at all in operation, so I think they might last a long time.


    • lui_gough says:

      Thanks for your in depth review! Acoustic noise in terms of beeps, squeals, buzzes, hums, ticks etc are not unusual from switching based converters where the inductors/transformers are wound loosely and the design somehow decides to oscillate in audible frequencies. Most better supplies will oscillate at higher ultrasonic frequencies so humans cannot perceive/be annoyed by them. I suspect the capacitors might last a good while as it may not be highly demanding temperature and ripple-current wise.

      – Gough

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