NiMH charger best life?

[SArepairman]

I bought some eneloop AA NiMH batteries, which are supposedly king of NiMH.

I don't want to blow 50$ on a high quality charger...
Can I just charge them really slow (like 0.1C or less) for a long time and still have the theoretical maximum battery life?
It would be free for me to setup 4 low current sources for charging for batteries... I am not in a rush to charge them.

[nuhamind2]

I bought a set of MQR06 (Sanyo quick charger) + 4 AA NiMH for only 30$.

[Kjelt]

I bought some eneloop AA NiMH batteries, which are supposedly king of NiMH.
Can I just charge them really slow (like 0.1C or less) for a long time and still have the theoretical maximum battery life?

Eneloop are King because they keep their charge for a long time (very low self discharge).
So why would you charge them for a long time and what do you find a long time.
Nothing wrong to charge an empty one the same way as 15 years ago, 14hrs on 0,1C.
But if they are half or more full then the access load will be transferred in heat which is not good for the cell. 0,1C it should survive (not much heat generated) but why if there are chargers that shut off on deltaV/t which cost $20 ?

[SArepairman]

Do you have a recommendation for a trustworthy 20$ charger?
I paid a bunch for these eneloops and I am worried that a cheap charger will mess them up...

[Kjelt]

Why not go with Sanyo's own Eneloop charger, usually they are in a package deal packed with 4AA batteries for around $30 but if you go to Ebay and search for "sanyo eneloop charger" you find them from $10 to $25 depending on the deal/country/shipping. 

[IanB]

It's tricky to find an inexpensive smart charger that has four individual charging channels and also has a reliable termination. Some chargers may sometimes miss the termination signal and overcharge a cell, and some chargers are oversensitive and may sometimes stop charging too early while a cell is barely 30% charged (this is bad if you use an under-charged cell in a group with fully charged cells). Other chargers have bad heat management and can overheat cells from their own electronics. Many chargers (including some Sanyo ones) charge cells in pairs, which is only helpful if you use the cells in the same pairing in equipment.

There are some who rave about the LaCrosse BC-700 or BC-1000, or the very similar AccuPower IQ-328. However, I think they have design weaknesses and poor heat management. For example the IQ-328 is specified to charge four AA cells at 1000 mA, but in my testing it was unable to do this without going into thermal shutdown and it made the cells very hot too. At a lower charging rate of 700 mA it copes better.

For my money the Maha C9000 is the best choice as a desk top, regular everyday charger. It has some flaws, but overall it just does what it is supposed to do in a reliable manner, day in, day out. Once you have got used to seeing exactly what your cells are doing and how they are performing, and exactly what state of charge they are in, you will find it hard to go back to a simple charger with no display.

That said, slow charging at 0.1C is an option and it will certainly work. In the long run, however, it may wear out your cells prematurely.

[peter.mitchell]

That said, slow charging at 0.1C is an option and it will certainly work. In the long run, however, it may wear out your cells prematurely.

I just thought I'd highlight this, most manufacturers state 16h at 0.1c is a proper method of fully charging the cells and that when cells are "fast" charged (0.5-1c) they are more likely to decrease in lifespan. Yes, if you leave them on the charger indefinitely they will lose capacity over time, but if you charge them correctly for 16h at 0.1c there should be no harm done.

[saturation]

I concur.  The Maha is also the only charger I know that will do the IEC 61951-2 c2003 to verify the true capacity of the battery; this is the procedure by which any official label on the battery mAH must be based on.

Based on the label and the Maha C9000, my eneloops and a Chinese LSD NiMH sold in the the US as Tenergy Centura, live up to their labels.

In addition, 3 years later, the batteries I quick charge using the Maha algorithms have not aged based on the IEC test, because I checked their IEC capacity when I first bought them, and rechecked them periodically.

I have a set of no-name NiMH that has reduced its aging rate after I began using the Maha on it, it was  2000 mAH when new in 2003, 1600mAH at the start in 2010, and 1400mAH 2 days ago.

The problem with a trickle charger is if it has no feedback circuits; no over temperature or end-voltage slope compensation.  The internal resistance in some batteries may rise temporarily so the battery's overheat during a charge; the response is to hold the charge until the battery's cool down even if the rate is 0.1C, unlikely as that seems. Repeated pulsing between charging and a no-charging state, this internal resistance may be dissipated thus, revitalizing an old battery, keeping old one's 'young'; its suspected to be caused by gas bubbles within the electrolyte that return into solution during the pulse charging effect.   So if you charge a battery using a passive constant current charge, and the cells temperature rises >=45^oC, this is total temp casing + ambient, the cells mAH will be reduced or cell destroyed.

During my evaluation of the Maha and since then, I've never had a battery charged go above 40^oC, at most its been < 38^oC measured with an IR thermometer calibrated against a Fluke thermocouple.

It is a magnificent technical charger; my only gripe with the C9000 is the user interface design.

For my money the Maha C9000 is the best choice as a desk top, regular everyday charger. It has some flaws, but overall it just does what it is supposed to do in a reliable manner, day in, day out. Once you have got used to seeing exactly what your cells are doing and how they are performing, and exactly what state of charge they are in, you will find it hard to go back to a simple charger with no display.

That said, slow charging at 0.1C is an option and it will certainly work. In the long run, however, it may wear out your cells prematurely.

[Jeff1946]

I bought the Eneloop 2 cell charger for travel since it works on 100-240 V.  I have used it many times here in the states and in Europe with no problem.  I like the Eneloops because I can charge them and leave them in my camera and not have to worry when I grab it if they are fully charged.  Some older types of NiMH batteries would lose at least 1% per day, I believe Eneloops lose about 10% per year.

[ben7]

I concur.  The Maha is also the only charger I know that will do the IEC 61951-2 c2003 to verify the true capacity of the battery; this is the procedure by which any official label on the battery mAH must be based on.

The IEC spec doesn't seem very realistic. No-one bothers to slow charge their batteries for 16 hours at 0.1C these days. Sanyo's own Eneloop chargers are rated for 8 or 4 hours depending on the cells, for example, so you can calculate C from that.

That isn't bad, compared to those silly 15 minute chargers. They absolutely kill the batteries!

I've had sanyo eneloops for almost 2 years now, I use the 4-cell eneloop charger too. Have had no issues whatsoever

[saturation]

Many battery standards have far less to do with application, but mostly on repeatability and consistency; the IEC is the standard, if you use any other method what can I say  You can read all about why in the IEC standards document.  Subject to your own application, your results will vary.  Like your car analogy, the hp of an engine is quoted by manufacturers without a body, transmission or actual road conditions, but it allows for a standard environment to compare just as IEC allows comparison from battery to battery, and manufacturers.

As for the applications, how have they held up?  I typically discharge them at 0.5-1A for run times ~ 2-4 hours, which means its consistent with IEC test.  I take them underwater to 100 meters, and use them ambient from -2 to  30^oC.  Both the tenergy and Eneloops hold up well, aging wise.  Besides not heating up during charging, I must add discharging so they don't overheat also prolongs life; above 1A rates, you should beware of overheating and even so, the AH rating declines substantially.  NiMH follow a similar curve as Peukert's Law for lead acid cells.

A word of warning on the Tenergy, they are not a large company like Panasonic who now own Sanyo.  So outside the USA, Chinese brand LSD NiMH is caveat emptor.

The IEC spec doesn't seem very realistic. No-one bothers to slow charge their batteries for 16 hours at 0.1C these days. Sanyo's own Eneloop chargers are rated for 8 or 4 hours depending on the cells, for example, so you can calculate C from that.