Searching for a smart AA battery charger

Over the years, I'm accumulated a large number of Ni-Mh rechargeable AA cells. These are in varying states of condition, wear and use, and I suspect some need to be thrown away.

I'm looking for a smart charger which will tell me their capacity, and in future do the best possible job of charging them. I have previously had batteries overheat using cheap chargers, so overheat protection is essential.

The current chargers I have come across are:

Nitecore D4 (~£24)
A relatively new charger - maybe hasn't had a chance to build up much of a reputation?
Both Ni-Mh and lithium batteries (a nice advantage) - although maybe sacrificing performance to do both?
No temperature cut off

Accupower IQ328 (~£25)
Small and neat AAA/AA charger
Temperature cut off
Capacity readout

Maha MH-C9000 (~£40)
Seems to have the best reputation of smart chargers
Temperature cut off
Lots of profiles
Maybe not the best as a general charger - better at analysis/cycling?


Do you guys have any thoughts or suggestions on these (or any other) battery chargers? The Nitecore looks very capable - however I'd be concerned it's Ni-Mh performance would be lacking due to it's high feature set and low price. The MH-C9000 does have an excellent reputation - although it is almost twice the price of the Nitecore, which is pretty steep.

The IQ328 might be a nice compromise of price and performance - but that's really just a guess!

Any comments or suggestions welcome .

Andy

Any will do try 7dayshop.com they are great and cheap as chips on there offers.

Having said all that, I've realised the Nitecore charger doesn't offer any discharging/analysis functionality. So that one is out of the equation!

If you want a larger list of analyzing chargers, check my website.
I have not tested the IQ328 charger, but at the current time I am working on one that looks about the same.

These are 2 of the better AA chargers.

http://www.candlepowerforums.com/vb...-Review-of-Analyzing-Charger-Powerex-MH-C9000

http://www.candlepowerforums.com/vb...est-Review-of-Analyzing-NiMH-La-Crosse-RS1020

cowana said:

Having said all that, I've realised the Nitecore charger doesn't offer any discharging/analysis functionality. So that one is out of the equation!

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You can enjoy the hobby without wearing the jacket,your torch will work no different to mine yet you will spend loads more on a charger than i will.

The Lacrosse BC700 or BC1000 are other options, about the same cost as a Maha C9000. The Maha can do the most, I think (more options for current in both charging and discharging) but it is almost twice the size of the BC700, if that matters to you.

The Maha C9000 seems to be the most recommended around here. My only complaint about it is that it caps the maximum voltage level at 1.47 volts. That is too low for Eneloops, and it terminates the charge too early, before the voltage dip occurs that a normal smart charger uses to stop the charging. The Maha compensates for the early termination by providing a 1 hour (or is it 2 hours?) top-up charge. But IMO that's a kludge and not the right way to charge a battery.

It would be much better if they would allow the user to set the maximum voltage level, which really should just be a safety trigger like temperature. I'd set it to somewhere between 1.55v and 1.60v for Eneloops. Also get rid of the top-up charge, since it would then do a proper -dV termination.

WalkIntoTheLight said:

It would be much better if they would allow the user to set the maximum voltage level, which really should just be a safety trigger like temperature. I'd set it to somewhere between 1.55v and 1.60v for Eneloops. Also get rid of the top-up charge, since it would then do a proper -dV termination.

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You are talking about the SKY charger.

HKJ said:

You are talking about the SKY charger.

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Yes, based on your review, that looks like quite the charger!

Hello WalkIntoTheLight,

The C9000 came out just before Eneloop cells were available in the US. There was a lot of criticism about changing the voltage termination from 1.6 volts down to 1.47 volts. Let's take a look at what you are giving up and what the advantages are.

Eneloop cells have been in use for several years now. When properly taken care of they last a long time. We do know that brand new cells can be destroyed in about a month when they are left on a charger that has a higher rate of trickle charge. This made us focus on the effects of over charging on these low self discharge cells.

There are two aspects of over charging. One is when the cell is continuously trickle charged at a higher charge rate, and the other is when there is a missed charge termination and the cell is charged at a higher rate. Missed terminations cause excess heat inside the cell and that causes problems with the low self discharge rate chemistry. The extended trickle charge seems to effect the chemistry inside the cell. The cells don't get hot or vent, they just loose capacity and the rate of self discharge increases substantially.

Normal NiMh cells can handle heat better and can withstand trickle charging for about a year with minimal damage.

The normal -dV charge termination results in increased heat in the cell when compared to terminating the charge based upon a voltage of 1.47. The question is how much difference does this make on cycle life and how does it effect the low self discharge characteristics of the cell.

I ran some tests utilizing a high charge rate and -dV termination to see how this extra heat would effect Eneloop cells. The result was that I was only able to get 150 cycles out of the cells and after those 150 cycles the self discharge rate over 30 days showed about a 10% drop in capacity. Granted this is testing at an extreme but it does give us an insight of how these cells perform.

The take away from this is that heat and extended trickle charging kills LSD cells.

Now let's look at what you are giving up.

I took 2 Eneloop cells, charged them at 1000 mA on the C9000, left them in the charger for another 2 hours to reach full charge, then discharged them at 1000 mA.

Average capacity was 1885 mAh.

I then took the same cells, charged them at 1000 mA, when DONE indicated the charge was complete I didn't leave them in for the top off charge but discharged them at 1000 mA.

The average capacity was 1820 mAh.

You are correct... If you pull the cells from the C9000 as soon as the charge has completed and before the top off charge, the cells will be less than fully charged by about 4%.

The question comes down to how often is it an inconvenience to let the cells go through the top off charge and how big an impact does that have on your intended use?

These cells were purchased 9 years ago and put into use in my camera. They get moderate use and have been mostly charged in the C9000. The initial capacity for the cells was 1935 mAh when new. After 9 years they are down almost 3%. I don't keep close track of cycles, but my "best guess" is that they have around 200 cycles on them.

Contrast that performance with the cells I mentioned earlier. Those Eneloop cells were charged in a charger that charged at 500 mA, utilized -dV termination, and trickle charged at 50 mA. The maximum voltage observed during charging was 1.6 volts. They were used in a flashlight and had less than 20 cycles on them when they died. They lasted about 2 months. The person using these cells had a concern about wanting to make sure he had the cells fully topped off for maximum run time so he left the cells on the charger all the time they were not in use.

You may think of the Maha algorithm as a "kludge," but it may actually be a forward looking wonderful design...

The Sky charger allows you to dial in your maximum voltage and that is a wonderful feature. Just be careful when deciding on the actual voltage to use and remember cells age and their charging characteristics change as they age. With new cells a lower voltage may work better and with older cells a higher voltage may work better. I am not sure if -dV termination is more reliable than 0 dV termination so that is another variable.

My experience indicates that terminating at 1.47 volts followed by a top off charge has no way inconvenienced my use of this charger. However, with that said the Sky charger looks very interesting...

Tom

The SKY uses both methodes, i.e. you might terminate on either -dv/dt or just voltage, maybe the Maha uses the same, but because the voltage is very low, you will never see the -dv/dt with eneloop cells.
One of the problems with voltage termination is that it varies with temperature (and cell chemistry), making it difficult to select the correct voltage. Maha has solved that by using a top off charge, but it is not guarantee that the cell will be fully charged at all temperatures (And brands).

The SKY charger is not perfect, I prefer the pulsing on the Maha, with a constant current.

SilverFox said:

Eneloop cells have been in use for several years now. When properly taken care of they last a long time. We do know that brand new cells can be destroyed in about a month when they are left on a charger that has a higher rate of trickle charge.

Normal NiMh cells can handle heat better and can withstand trickle charging for about a year with minimal damage.

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Do we understand why this is the case? What is it about the chemistry of LSD cells that causes them to be damaged more easily by trickle charging?

I ran some tests utilizing a high charge rate and -dV termination to see how this extra heat would effect Eneloop cells. The result was that I was only able to get 150 cycles out of the cells and after those 150 cycles the self discharge rate over 30 days showed about a 10% drop in capacity. Granted this is testing at an extreme but it does give us an insight of how these cells perform.

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That is a surprising result. I've always used various smart chargers that do -dV termination, and have never had a problem with my Eneloops, some of which are 8 years old. Are you sure it was the -dV termination that caused your cells to deteriorate, or was it really the high charge rate (what did you use?) that would have killed them whether you used -dV or a max voltage of 1.47v ?

If you pull the cells from the C9000 as soon as the charge has completed and before the top off charge, the cells will be less than fully charged by about 4%.

The question comes down to how often is it an inconvenience to let the cells go through the top off charge and how big an impact does that have on your intended use?

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My concern was not really about getting a full charge. It was more about whether or not the 2-hour top-up would eventually cause damage to Eneloops, because they don't like to be over-charged. But it sounds like you haven't seen any bad effects from letting it do that.

Hello WalkIntoTheLight,

I don't have a clear answer but the best guess is that the problem has to do with a change in the chemicals used in the LSD cells. Normal cells are trying to self discharge and that rate equalizes the trickle charge rate. The LSD cells don't self discharge so the trickle charge just overcharges the cells.

-dV is a great way to terminate a charge as long as the proper values are used. The problem comes with a missed termination. It seems to all come down to the heat generated within the cell. -dV termination generates more heat in the cell than terminating at 1.47 volts followed by a trickle charge.

The charger I used for the extreme testing was the Energizer 15 minute charger. It was charging at around 8000 mA. It also has a very robust termination algorithm that includes a 3 mV -dv, maximum temperature, and time limit. Cell temperature was actually less than some hobby chargers charging NiMh battery packs at 2C. The cells were very worm but not hot. I was actually impressed that the Eneloop cells lasted 150 cycles.

On the other hand I was concerned that a couple of months of 50 mA trickle charging did totally destroy the Eneloop cells.

Over the years I haven't seen a problem with the top off charge and I keep pretty close track of the performance of my cells.

Tom

SilverFox said:

The charger I used for the extreme testing was the Energizer 15 minute charger. It was charging at around 8000 mA. It also has a very robust termination algorithm that includes a 3 mV -dv, maximum temperature, and time limit. Cell temperature was actually less than some hobby chargers charging NiMh battery packs at 2C. The cells were very worm but not hot. I was actually impressed that the Eneloop cells lasted 150 cycles.

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Ouch! An 8 amp charge current! I'm surprised they lasted 150 cycles too. Well, good to know. I guess that means a charge current of 2 amps shouldn't be too hard on them, if I need a charge in an hour.

SilverFox said:

I am not sure if -dV termination is more reliable than 0 dV termination so that is another variable.

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The chances of a missed termination with -dV termination will always be higher than with 0dV. The -dV signal will always be preceded by a 0dV signal (i.e. the voltage slope has to level off before it can drop off)

0dV should generally be fairly reliable, but I have heard of cases where the voltage on old cells continued to climb very slowly instead of leveling off - obviously, the voltage can't continue climbing forever, so a charger using this method would eventually terminate, but the cell could still end up being overcharged.

Personally, I think that the inflection method is even better - it works reliably - even when charging old cells at low rates. It terminates the charge just after the cell starts to warm up, so it's not overheating the cell excessively. The only slight downside is that the cells end up slightly undercharged compared to -dV, but I think it's worth it for the increase in cell life.

The following image best illustrates the above:



I've written up a forum post here which includes a bit more detail on the inflection method and why I've used it in the UltraSmartCharger:
http://www.ultrasmartcharger.com/phpBB3/viewtopic.php?f=3&t=5

Although your graphic illustration shows a true mathematical inflection point (where the curvature goes from concave up to concave down) your description sounds more like you are looking for a particular slope value compared to earlier rather than the slope going from increasing to decreasing. Can you clarify that point please?

inetdog said:

Although your graphic illustration shows a true mathematical inflection point (where the curvature goes from concave up to concave down) your description sounds more like you are looking for a particular slope value compared to earlier rather than the slope going from increasing to decreasing. Can you clarify that point please?

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Sure - the method that I'm using isn't strictly terminating at the inflection point, but at the point where the slope has dropped to half the maximum.

Trying to stop right on the inflection point would be basically impossible due to measurement errors, and it would result in a reasonably significant undercharge.

Thanks. That was my impression, but I wanted to confirm that. The graphics seem misleading since none of them showed anything but the inflection point.
I would call the algorithm "post-inflection-point" instead.
The very clear change in the behavior of the slope, however you detect it, does look like a very robust indicator, and one which cannot really be missed. It does help to have a microprocessor to do the calculation though.

WalkIntoTheLight said:

The Maha compensates for the early termination by providing a 1 hour (or is it 2 hours?) top-up charge. But IMO that's a kludge and not the right way to charge a battery.

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When "done" appears, it will provide a 60ma charge each hour. Once two hours has passed, the 9000 will do a TRUE trickle of only 10ma an hour. Maha is about the only manufacturer that seems to know the difference between trickle and slow charge. Most others that claim trickle are in fact doing a slow charge, and doing a slow-roast on the cells.

But, what is the obsession over an extra 60-100ma at the top end? Will that really make a difference to your application? What I see in the field is that the average consumer tends to treat his cellphone battery better than we do with frequent and many times incomplete top offs, (different chemistry obviously) whereas we obsess over 100% SOC and run the cells through full charge / discharge cycles all the time.

I understand the desire for having an individual cell charger like the 9000 (I have one and love it!) also do balancing by reaching 100% SOC on each cell individually, but does one really need to do this each and every cycle? No - unless your application was very under-budgeted for power use to begin with - or you are using CRAP cells.