Sanyo 2700 vs Eneloop Discharge test @ 45, 60, 75 and 90 days

[odessit]

Since I did not find a clear test on Eneloop vs Sanyo 2700 discharge rates and performance, I made my own test.
Please note, to simulate worst case scenario I am saving batteries with lowest charges until the end.

1. Charged on Maha 9000 Break-In cycle.
2. Stored around 17-20C
3. Discharged on Orbit Pocketlader charger/analyzer at 500mA

                      Eneloop 2000mAh  Sanyo 2700mAh
45 day test is done          2048mAh | 2553mAh   
63 day test is done          2018mAh | 2544mAh
75 day test is done          1977mAh | 2521mAh
90 day test is done          1973mAh | 2515mAh

45 day test
           Initial | Final-mAh | Final-mWh | mAh-lost | %mAh-lost | Runtime      
Eneloop2k  2048    | 1840      | 1958      | 208      | 10.2%     |  252 m  
Sanyo2700  2553    | 2348      | 2494      | 205      |  8.0%     |  317 m  

60 day test
           Initial | Final-mAh | Final-mWh | mAh-lost | %mAh-lost | Runtime      
Eneloop2k  2018    | 1813      | 1926      | 205      | 10.2%     |  254 m  
Sanyo2700  2544    | 2245      | 2407      | 299      | 11.8%     |  303 m 

75 day test
           Initial | Final-mAh | Final-mWh | mAh-lost | %mAh-lost | Runtime      
Eneloop2k  1977    | 1852      | 1923      | 125      |  6.3%     |  268 m  
Sanyo2700  2521    | 2198      | ----      | 323      | 12.8%     |  316 m 

90 day test (Please note, Sanyo 2700 test was technically 12 hrs too early)
           Initial | Final-mAh | Final-mWh | mAh-lost | %mAh-lost | Runtime      
Eneloop2k  1973    | 1855      | 1920      | 118      |  6.0%     |  270 m  
Sanyo2700  2515    | 2198      | 2324      | 317      | 12.6%     |  304 m

Note, the test is not very scientific:
Sample size is very small and relies on individual cells to provide idea about the whole line.


45 day self discharge graph

63 day self discharge graph

75 day self discharge graph - Eneloop Only.

90 day self discharge graph

Dark red - Sanyo 2700 voltage
Light red - Eneloop voltage
Dark blue - Sanyo 2700 discharge current
Light blue - Eneloop discharge current

If you have any ideas on how to make this test better, please let me know.

 

[bob_ninja]

Re: Sanyo 2700 vs Eneloop Discharge test

If possible, I have a suggestion.
For the tests use cells with minimum 50 cycles on them as opposed to brand new. Just pick some cells that have some service 100+ cycles.
I find higher capacity cells tend to degrade and loose capacity rapidly, so the typical performance is far below that of a new cell.

 

[etc]

Re: Sanyo 2700 vs Eneloop Discharge test

Looks like you have to store these cells for a long time to realize the benefits, even at 90 days Sanyo is still the winner.

I have Maha Powerex 2700 mAh and they discharge pretty slow also, even not being LSD cells.

 

[odessit]

Re: Sanyo 2700 vs Eneloop Discharge test

These are the only ones I have.
I can also run 100 charges/discharges on a single cell (I can set Orbit to do 9 discharge/charge cycles), but it will take a week with very high charge/discharge currents (4 amp charge/discharge)

If somebody has these batteries with some use on them, I can "age" them and run tests, but to be fair, the # of cycles should be close between all batteries.

Edit - will a battery after a week long, 4 A charge/discharge marathon be qualified as "used" battery or abused battery? Any practical benefits for me to try this or just curiosity to see if I can get couple batteries to vent?

 

[odessit]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45 and 63 days

Updated OP with 63 day discharge test table and graphs.
Non LSD Sanyo 2700 is starting to show it's weakness, but still leading by a healthy margin.

 

[IMSabbel]

Re: Sanyo 2700 vs Eneloop Discharge test

If possible, I have a suggestion.
For the tests use cells with minimum 50 cycles on them as opposed to brand new. Just pick some cells that have some service 100+ cycles.
I find higher capacity cells tend to degrade and loose capacity rapidly, so the typical performance is far below that of a new cell.

Most people wont ever get 100 cycles on those batteries (think about its, thats 4 years if you recharge them every forthnight), so i do not think you should stack the deck to much towards the eneloops.

 

[bob_ninja]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45 and 60 days

100 cycles is not the point.
I have Sanyo 2500s and some developed high SD after only 20-40 cycles. Could be accidental deep discharge or high load or something else, not sure. Meanwhile Eneloops are handling all sorts of abuse and not developing high SD.

So my point is that the more complete analysis would include comparison of an Eneloop against a high SD Sanyo.

That being said there are some 2700s like Powerex that are more robust and tend to maintain low SD.

 

[yellow]

wow, Your normal cells are great

I just tossed a whole bunch of mine, because they loose even with just a few days / up to a week of storage
dunno how often they were used, guess considerably under 50 times (because I mainly use 18650 for 1.5 years now), but they were aged at about 1 year.

 

[f22shift]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45 and 60 days

what rate are you guys charging your sanyo 2700? i know that a lower rate is better for life but i remember reading to charge at a rate that would finish it in 1-2 hrs which is a rate that is pretty high.

 

[SilverFox]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45 and 60 days

Hello F22shift,

If you look up the data sheet on the Sanyo 2700 cells, it shows expected capacities when discharging at various rates. The charge rate used for those graphs is 2500 mA using -dV value of 10 mV.

If you want good performance from your 2700 mAh cells, charge them at 2500 mA and set your termination -dV to 10 mV.

Fast charging does impact cycle life, but in this context, fast charging means charging in 15 - 30 minutes. Normal charging completes the charge in a little over 1 hour. Slower charging completes the charge in a little over 2 hours.

Of course form charging does not rely on cell performance to terminate the charge. The charge is terminated with a timer after 16 hours. The 0.1C charge rate is set to minimize any damage due to overcharge to the cell.

I believe Sanyo uses 1C charging (completing the charge in a little over 1 hour) in their determination of expected cycle life.

Tom

 

[bob_ninja]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45 and 60 days

what rate are you guys charging your sanyo 2700? i know that a lower rate is better for life but i remember reading to charge at a rate that would finish it in 1-2 hrs which is a rate that is pretty high.

I am in the slow charge camp, so use between 500mA and 700mA for my Sanyo 2500s and Powerex 2700s, usually 500mA for Eneloops. For older cells I may go to 1A. Also when using Maha's 9000 I tend to use higher rate, about 1A.

So my charge rates are about 0.3C, pretty slow.

I used Eneloops in remote cars and even a swing for the baby. These would be higher load applications I can think of. I marked a set of 4 Eneloops that I "abused" using them for these higher load applications. They are still fine.

On the other hand I have a small number of Sanyos develop a high SD. Not sure when and how since I try to use Eneloops for more demanding stuff. I am guessing that Sanyo were in devices that were left on and are too dumb to switch off automatically. For instance, walkie talkie that my wife often forgets to switch off used Sanyos. So both Sanyos and Powerex could end up being discharged too low, below 0.9V

Also no Powerex has failed yet, although Sanyos are the oldest.

So my point is to test cells (Eneloop and Sanyo) after they had a couple of "accidents" that are common, happen all the time. So perhaps they get discharged below 0.9V or perhaps you use them in a high load device for a bit, etc. That would simulate real world better, provide a more realistic comparison of SD and charge retention.

 

[odessit]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45, 60 and 75 days

Updated 75 day self discharge test data. Sanyo 2700 is still leading.
Sorry, I only have the final mAh and time values for this Sanyo 2700. Discharge graph was wiped out during Windows Update reboot

 

[UnknownVT]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45, 60 and 75 days

Updated 75 day self discharge test data. Sanyo 2700 is still leading.

Thank you for your work.

It is interesting how well the Sanyo 2700mAh has kept its charge - despite of some negative reputation.

Just wanted to point out the apparent anomoly -

at 75 days the eneloop loss at 6.3% mAh -
was lower than at 45 or 60 days -

45 days loss 10.2%
60 days loss 10.2%

So it is hard to intepret the results -

eg: the implication is that eneloop gains capacity for storing an extra 15 days after 60?

also those two latter figures seem to imply there was 0% loss between 45 and 60 days?

Please note I am not doubting your results -
Perhaps this is possibly due to simple sample variation?

 

[Mr Happy]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45, 60 and 75 days

Just wanted to point out the apparent anomoly -

at 75 days the eneloop loss at 6.3% mAh -
was lower than at 45 or 60 days -Please note I am not doubting your results -

Perhaps this is possibly due to simple sample variation?

I noticed that too. I suspect it is because there are four separate cells under test, all charged at beginning and discharged one by one? Therefore sample variation would indeed explain it.

 

[odessit]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45, 60 and 75 days

In a scientifically accepted test we should have large sample size and random ordering. So you are correct, the sample size is too small. However, there may be another explanation:

I used cells with highest initial capacity first. Perhaps these cells accepted an overcharge - thus higher self discharge rate in the beginning.
I am saving the batteries with the smallest initial charge until the very end. These cells are the closest to the "optimal" capacity, thus self discharge is lower.

Is this theory close or am I completely off the mark?

 

[etc]

Re: Sanyo 2700 vs Eneloop Discharge test @ 45, 60 and 75 days

Thansk for the research.

 

[odessit]

Ok, 90 day test is done.
Brand New Sanyo 2700 is still winning.

Eneloop graph is a bit screwed up for the first 205 mAh due to a poor contact (fixed at 205 mAh mark)

 

[SilverFox]

Hello Odessit,

Very interesting results...

There are some things that strike me as being a little bit strange. Perhaps you can help me figure them out.

If I understand your set up correctly, you are discharging at 500 mA. I am used to seeing Eneloop cells have a mid point voltage of about 1.28 volts when being discharged at that rate. The Sanyo 2700 mAh cells that I tested had a mid point voltage of 1.24 volts at that discharge rate. If I am reading your graphs correctly, I am seeing mid point voltages below around 1.1 volts for both cells.

I am also not sure what your blue discharge lines are showing. It looks like the discharge line starts at a - 0.5 amps, then starts increasing at about 2/3 into the test and ends up around a - 0.04 amps.

The very interesting observation has to do with the discharge rate you are seeing with the Sanyo 2700 mAh cells. The amount of self discharge you are reporting is almost exactly the same as the amount (in percent) that I saw with the Eneloop cells at the 90 day point.

IF your test results are accurate, one might SPECULATE that Sanyo may have produced some 2700 mAh cells using some of the low self discharge rate chemistry...

Others have commented on the self discharge rate of 2700 mAh cells, and what you are seeing at 90 days, they have reported at 30 - 45 days. Theoretically, given a constant 0.7% per day self discharge rate for normal NiMh chemistry, you 2700 mAh cells should be at around 55 - 60% of their initial capacity after 90 days of self discharge.

I am not sure what is going on, but it is very interesting. Do you happen to remember where you picked up the 2700's from? Do they have any kind of date code?

Very interesting results...

Tom

 

[45/70]

Nice job, odessit! I've been keeping an eye on this thread. Interesting results.

As others have mentioned, I think the Sanyo eneloops would win after x amount of cycles. How many? From my somewhat limited experience with various high cap NiMhs, not too many, but I'll leave that open.

What intrigues me, is something I never really considered. It would be interesting to see a comparison of the Sanyo 2700's to L91's. A lot of folks use lithium primary AA's for their ability to maintain their capacity and supply superior current (compared to alkalines) for a ridiculously long time. Your work suggests however, that for non-voltage dependent applications, the Sanyo 2700's may be a viable alternative. This would only apply for relatively short terms of 90 days, but possibly longer. I'm sure I'm not the only one that uses L91's in this way.

I don't doubt in this suggested comparison, that the L91's would win. Still, consider the similar capacity, the fact that you can recharge the NiMh's at least several times before self discharge increases, similar performance, and add to that, the cost of cells being about the same.

When the self discharge reared it's ugly head, you could just press the 2700's into regular service, or give them away. You would still come out ahead. Humm..... :thinking:

Dave

 

[Anders]

Hello Odessit.

Thanks for the hard work, interesting results indeed.

But as Silverfox pointed out, curious graphs, in my previous tests with Maha Imedion, the mid point voltage was 1.26 @ 0,5A.

Anders