AA cells for high cycle count

Hi, I am working on a project. (actually its a gift for my wife )

For various reasons I want to power it with AAs if possible. One of those reasons is that normally it will run on rechargeable batteries most of the time, but can also run on AA energizer Li in a pinch.

The power draw is not all that high (4 cells in series) x ~ 0.1 - 0.2 amps, but it will run more or less all day and has to be portable. There will be 2 packs inside in parallel to meet the run time goal and selected with a switch.

The plan is to recharge it every night with the batteries in the pack, so still 4S, because it requires a screwdriver to access the batteries.

Ideal battery capacity is ~ 2000 mahr or similar.

LSD cells are ok , but obviously not any benefift.

Based on the results of aacycler.com, none of the AAs that are in this ~ 2000 mah range will really last more than 3 months. That is acceptable but I wonder if there are better options out there, such as NiCd or similar?

The FDH cells that are getting extremely long cycle life are only about 1/2 of the needed capacity.

I am not all that worried about the cost per cell, but I need to be able to buy them on-line in the US.

Feel free to point me toward a tester / review site.

I am already reading aacycler.com test results, which are mostly related to LSD type cells.

Also looking at the battery comparator site.

https://lygte-info.dk/review/batteries2012/CommonAAcomparator.php

Great info BTW.

At all long time ago, when LSD cells were not existing, high capacity NiMH cells had one problem, a high self discharge rate. There is one rule for non LSD high capacity cells: "The higher the capacity, the higher the self discharge". I had normal high capacity NiMH cells and they were empty after a few weeks after charging and not using it.

At all there is no reason not using LSD cells, if you are forced to use NiMH cells. NiCd are difficuild to find and I would say a single AA NiCd cell will have less than 1000mAh capacity.

Maybe you thing about using a 18650 LiIon cell as source. The capacity of LiIon cells is much higher for the same volume. You can integrate a small charging circuit into your device and than also the device that contains the Liion cell only needs to plugged in. There should be charging circuits available in the all known china stores. I even guess there are circuits that will be USB powered, that would make everything easier....

WarriorOfLight said:

At all long time ago, when LSD cells were not existing, high capacity NiMH cells had one problem, a high self discharge rate. There is one rule for non LSD high capacity cells: "The higher the capacity, the higher the self discharge". I had normal high capacity NiMH cells and they were empty after a few weeks after charging and not using it.

At all there is no reason not using LSD cells, if you are forced to use NiMH cells. NiCd are difficuild to find and I would say a single AA NiCd cell will have less than 1000mAh capacity.

Maybe you thing about using a 18650 LiIon cell as source. The capacity of LiIon cells is much higher for the same volume. You can integrate a small charging circuit into your device and than also the device that contains the Liion cell only needs to plugged in. There should be charging circuits available in the all known china stores. I even guess there are circuits that will be USB powered, that would make everything easier....

Click to expand...

Thanks. 4 x 1.2 volts is already on the voltage low end for this project, so it would take at least 2 S of the 18650s.

I might do that some day but this is for a gift, not a high volume production project.

If possible, I am looking for either a North America or EU source for cells.

One possibility is the ansmann 2800. It isn't a LSD and even though it is not looking like anything special from a cycle count perspective, 2 packs of those have a high enough capacity to potentially avoid needing a "full cycle" each day.

Dont take ansmann 2800 cells. Those would loose capacity really fast.
The cells you want are the light blue eneloop lite ones. To rise the capacitry (if required) just connect some of those in parallel. Those eneloop lite cells are to my experience the cells with the highest cycle count and the most stable chemistry i have ever seen and used.

nqhzdkdf said:

Dont take ansmann 2800 cells. Those would loose capacity really fast.
The cells you want are the light blue eneloop lite ones. To rise the capacitry (if required) just connect some of those in parallel. Those eneloop lite cells are to my experience the cells with the highest cycle count and the most stable chemistry i have ever seen and used.

Click to expand...

Thank you for the suggestion.

Unfortunately, the battery that you are suggesting does not appear to be very available any more.

Take a look at aacyler.com's ongoing test of that ansmann 2800 cell. Preliminary results indicate a viable 100 cycle lifetime.

100 cycles will provide 100 days of operation, charged daily. This will result in replacing them 4 times per year (4 batteries per pack) so only 16 batteries per year and the weight of just 4 batteries.

That is just $6 / month in battery cost to keep my wife happy. Seems like a bargain.

If I design it with the 1000 ma cells, it would require the device to carry at least 8 cells (maybe even 12) for the run time instead of 4 - for instance using the FDK HR-AAULT

If my wife likes the gift and really uses it, then I can always redesign it with a Li pack for higher cycle count operation.

The battery cost is honestly only a small part of the total cost of hand building an electronics device good enough to give to your wife on Mother's day. I am already on rev 5.

The ansmann cells arrived today (both the slimline 2850 and the AAA equivalent. Also purchased their 8 position charger so that I would have at least something to use on them.

Don't have any method of discharge testing them to see what they will actually do under the relatively small load, so I need to think about that aspect.

It would be nice to have simple way to sort them out as they decay.

Harry

In case anyone is interested:

1) In very fine print, sometimes only on the batteries and not on the packaging - made in China

2) Hot off the charger they were ~ 1.4 volt with some variations.

Like many batteries, the surface charge decays away and within 12 hours both the AAA and AA are all at 1.37 +/- ~ 0.1 volts.

I am glad that I bought the slimline version because they were pretty much a perfect fit in the battery holder that I have.

I am looking for someone to do some 4 cells in series pack type testing for me under conditions similar to the intended charge / discharge conditions posted for ~ 100 cycles.

I just don't have the time nor equipment and am looking for someone who does.

My primary interest is if they will stay relatively well balanced when charged in a pack like this at ~ 25, 50, 75 and 100 cycles.

Willing to cover any related costs.

Thanks

Harry

I forgot to mention that in the US the cells are sold by bhphoto.

Quick update.

Using the AAAs in the roku remote control(s) and they seem to last just as long as the other primary batteries we were using - or close enough.

Starting to use the AAAs in a modest power headlamp that gets used a lot to find parts on shelves. Again - relatively low drain currents which is what these seem to be designed for.

Have not run a lot of cycles on any of them but with low current uses so far there haven't been any obvious issues.

I don't make any attempt to keep them sorted. I have a small box of them in the garage and just rotate them through the charger to keep them topped off when I think about it.

This is the link to AACycler's very helpful test of this cell. - Thank you very much for doing this testing. Great resource.

http://aacycler.com/battery/aa/ansmann-2850/