Sanyo 2700 vs Eneloop - 100 Charge Cycles Analysis

odessit · Feb 12, 2009

I am done with 100 cycles on 1 Eneloop and 1 Sanyo 2700

Code:

Number of Cycles:          100
Charge Current (mA):       2000
Discharge Current (mA):    1000
Data Recorded:             mAh
Previous Charges(#0):      1 Break-in Cycle on Maha C9000

Cycle   Sanyo2700   Eneloop2000
0        2570          1921
1        2440          1897      
2        2334          1845      
3        2319          1825      
4        2323          1805      
5        2335          1820      
6        2319          1826      
7        2299          1807      
8        2318          1804      
9        2307          1833      
10       2316          1824      
11       2318          1812      
12       2316          1815      
13       2421          1865      
14       2386          1801      
15       2351          1814      
16       2350          1812      
17       2346          1823      
18       2331          1828      
19       2313          1808      
20       2343          1810      
21       2333          1825      
22       2321          1815      
23       2311          1808      
24       2313          1825      
25       2404          1865      
26       2315          1817      
27       2306          1820      
28       2303          1815      
29       2296          1810      
30       2302          1814      
31       2314          1827      
32       2299          1814      
33       2306          1806      
34       2279          1810      
35       2257          1825      
36       2287          1812      
37       2383          1884      
38       2291          1805      
39       2280          1822      
40       2262          1814      
41       2271          1810      
42       2269          1813      
43       2266          1828      
44       2268          1823      
45       2270          1815      
46       2252          1804      
47       2242          1820      
48       2274          1824      
49       2386          1876      
50       2272          1830      
51       2271          1833      
52       2258          1838      
53       2273          1822      
54       2265          1809      
55       2272          1822      
56       2272          1835      
57       2253          1826      
58       2242          1815      
59       2244          1817      
60       2237          1832      
61       2379          1872      
62       2290          1806      
63       2285          1807      
64       2267          1792      
65       2264          1806      
66       2268          1815      
67       2271          1816      
68       2265          1796      
69       2241          1800      
70       2252          1816      
71       2213          1806      
72       2205          1808      
73       2386          1866      
74       2209          1813      
75       2231          1809      
76       2214          1811      
77       2221          1808      
78       2202          1810      
79       2245          1808      
80       2216          1813      
81       2213          1807      
82       2216          1804      
83       2227          1800      
84       2216          1808      
85       2284          1868      
86       2232          1790      
87       2217          1807      
88       2234          1810      
89       2203          1799      
90       2201          1792      
91       2182          1800      
92       2196          1803      
93       2180          1801      
94       2204          1783      
95       2193          1795      
96       2192          1789      
97       2247          1857      
98       2175          1789      
99       2221          1790      
100      2179          1788

The strange "peaks" are occurred at each cycle#1, I believe this is because MAHA C9000 tries to top-off already full cells.

I will also do a discharge graph at 0.5A on each cell to find mAh and mWh.
What other statistical analysis can I do?
Would a 90 day self discharge test be OK or should I go lower?

EDIT, I forgot to mention - I was informally monitoring voltages on each charge. They never went below 1.4V

NiOOH · Feb 15, 2009

odessit said:
I almost done with 100 cycles on 1 Eneloop and 1 Sanyo 2700 (currently in mid and high 90s)
Here is a quick outline:

Code:

Number of Cycles: 100 Charge Current (mA): 2000 Discharge Current (mA): 1000 Data Recorded: mAh Previous Charges: 1 Break-in Cycle on Maha C9000

I will post raw data and the graph with trend line.
I will also do a discharge graph at 0.5A on each cell to find mAh and mWh.
What other statistical analysis can I do?
Would a 90 day self discharge test be OK or should I go lower?

Looking forward to see your data. IMO 90 days is a bit too long for the 2700 mAh cell. Perhaps an initial test at 30 days will be be better.

odessit · Feb 16, 2009

Updated OP with charge data. I will run discharges early this week.

NiOOH - What is the exact reason for 30 days?
I do not think that 90 days is too long. In my "new battery test" after 90 days, Sanyo 2700 still had more juice than Eneloop.
Also, on another website, Sanyo 2700 survived 6 month discharge with more mAh than any LSD battery. (these are for brand new cells)

NiOOH · Feb 17, 2009

odessit said:
Updated OP with charge data. I will run discharges early this week.

NiOOH - What is the exact reason for 30 days?
I do not think that 90 days is too long. In my "new battery test" after 90 days, Sanyo 2700 still had more juice than Eneloop.
Also, on another website, Sanyo 2700 survived 6 month discharge with more mAh than any LSD battery. (these are for brand new cells)

Thanks for the data odessit!

I suggested 30 days just to check if the 2500 mAh cell has developed high self-discharge it is prone to. If you run 90 days test, the cell may have discharged in a couple of weeks, even couple of days. If there is no reason to believe that the high capacity cell has a high self-discharge, 90 days is OK.

odessit · Feb 17, 2009

of course, early graph is better than no graph...

bretti_kivi · Feb 17, 2009

but what does this say to us?

2700s decline slightly faster than eneloops, but they have 20% more capacity to start with.
Or at least, this one did.
What was the charging rate?

Bret

jtr1962 · Feb 17, 2009

bretti_kivi said:
but what does this say to us?

2700s decline slightly faster than eneloops, but they have 20% more capacity to start with.

And according to those equations, after about 400 cycles the Eneloops start to pull ahead.

baterija · Feb 17, 2009

jtr1962 said:
And according to those equations, after about 400 cycles the Eneloops start to pull ahead.

Assuming they both retain a linear decrease in capacity.

It's also interesting to note that the Eneloop are at about 78% capacity and the Sanyo 2700 at 79% capacity - so both would have passed the recycle criteria some here use before that change over happens. Those percentages would be even worse based on rated capacity, or the actual first cycle, instead of the formula capacity I used to compute them too.

555BUK · Feb 17, 2009

baterija said:
Assuming they both retain a linear decrease in capacity.

It's also interesting to note that the Eneloop are at about 78% capacity and the Sanyo 2700 at 79% capacity - so both would have passed the recycle criteria some here use before that change over happens. Those percentages would be even worse based on rated capacity, or the actual first cycle, instead of the formula capacity I used to compute them too.

Not sure what you are saying
*Sanyo 2700 capacity after 100 charges = 2179mAH/2700mAh*100 = 80.7%
*Eneloop capacity after 100 charges = 1788mAh/2000mAh*100 = 89.4%

Both look pretty good to me, but the Eneloop is the clear long-term keeper.

bretti_kivi · Feb 17, 2009

I'd be wary of drawing such conclusions, mainly because:

- it's one cell of each type, not multiple
- it may be different using a different charge rate
- were they fresh cells? how could we find this out?

This should start to highlight the problems with doing reliable, sensible tests. I like the stats, but I don't see that they have much applicability.

Bret

baterija · Feb 17, 2009

555BUK said:
Not sure what you are saying
*Sanyo 2700 capacity after 100 charges = 2179mAH/2700mAh*100 = 80.7%
*Eneloop capacity after 100 charges = 1788mAh/2000mAh*100 = 89.4%

Both look pretty good to me, but the Eneloop is the clear long-term keeper.

My comparison was at cycle 397 where linear decays in capacity have them approximately equal. I also used the same formula to compute cycle zero capacity for the percentage comparison instead of using nominal capacity. Nominal capacity would have made the cells retained capacity percentage look even worse.

Bret - I agree that the small sample size of one does have limited utility. It is interesting that it doesn't invalidate the rule of thumb about using the higher capacity cells if your usage is overwhelmingly fresh off the charger. One data point beats what basically was no data points before. :naughty:

bretti_kivi · Feb 17, 2009

baterija said:
One data point beats what basically was no data points before. :naughty:

Very true, I'm just wary about drawing lots of conclusions

I've been using Sanyos for ... six years? They get replaced after 1-2 years as a matter of course. One set of old 2500s was crap from the start; the present ones (3 sets) - two sets are excellent, one is OK. I tend to top them off on the charger before throwing them in the flash. An ancient 1700 still has a place in my wireless mouse at work

Bret

odessit · Feb 17, 2009

The purpose of this test was to be just another data point. Hopefully this will be verified by other people.

To address some of the comments:
Even if I would have done multiple cells(4), they would be from the same batch. We need more people to do these tests! There are plenty of people with Maha C9000 that can easily verify this information.

These are unused cells:
Sanyo 2700: 07-10 SH
Eneloop 2k: 07-07 IO

Since the curve may not be linear:
Exponential function:
Sanyo 2700: y = 2356.5e^-0.0007x
Eneloop 2k: y = 1829.9e-0.0001x

Power function:
Sanyo 2700: y = 2441x^-0.0193
Eneloop 2k: y = 1845.4x^-0.0042

jtr1962 · Feb 17, 2009

555BUK said:
Not sure what you are saying
*Sanyo 2700 capacity after 100 charges = 2179mAH/2700mAh*100 = 80.7%
*Eneloop capacity after 100 charges = 1788mAh/2000mAh*100 = 89.4%

Both look pretty good to me, but the Eneloop is the clear long-term keeper.

I'd probably use 80% of initial measured capacity rather than labeled capacity as a criterium for recycling. In that case I get:

Eneloop: 1788/1921 = 93.1%
Sanyo 2700: 2179/2570 = 84.8%

If the capacity continues to decay linearly then the Sanyos will reach 80% ( 2056 mAh) at 191 cycles but the Eneloops will be fine until 1197 cycles.

On another note, even when cells reach the criterium for recycling they often are still good for low drain applications like wall clocks. I've found that cells which might be crap under heavy loads have nearly full capacity under loads of a few mA. If a cell develops internal shorts or high self-discharge then of course it's useless.

etc · Feb 17, 2009

thanks for the chart.

bob_ninja · Feb 18, 2009

Actually these results tell as a great deal.

For instance I remember instances of marketing being mentioned on this forum regarding lifespan being hundreds of cycles (don't remember particulars now, LSD or conventional, etc.) We were discussing deceptive marketing and vague promises regarding lifespan.

Yet here we have degradation to about 80% for a conventional high capacity cell after only 100 cycles!!! So any claims of hundreds of cycles should NOT be trusted without actual test data.

Also it shows that LSDs like Eneloop clearly hold up better and should have a longer lifespan than high capacity types. In particular, it demonstrates that they handle discharge rates better. This is just a confirmation of the empirial evidence we have. Such as my mom using Sanyo 2500 in her camera only to develop extreme SD after about 2 years of casual use. Thus I gave her Eneloops to replace them.

I would be curious which one does most/more damage: 2A charge or 1A discharge? Tom did tests with 15min chargers showing little damage from very high charging current. I just wonder if results would be any different using a slower say 0.5A charge current (despite not being safe, etc.....)

Also, these results tell is that it is rather difficult to obtain hundreds of cycles from AA NiMH. Compared to LiPo tests using A123 cells that were cycled hard for about 1000 cycles at which point they were at 80% capacity, these results are rather dissapointing!!!!

My own conclusion is that NiMH is to be avoided as much as possible for any application over 0.3C draw. So general electronics like radios, MP3 players, ordinary flashlights are fine. Any power tool should probably be using new LiPo type batteries. NiCd is probably not worth the trouble any more.

It als tells me that LiPo cells are probably worth paying 2x and 3x more than NiMH for power tools and other high current applications.

Of course, thanks for all the work. Great stuff

As others said, test SD anything between 30-90 days would be fine.

P.S.: Another important factor besides how much capacity dropped is SD. Even at 80% for 2700s, if at this point it has a high SD then it is useless. So both remaining capacity and SD are significant (after 100 cycles)

bob_ninja · Feb 18, 2009

bretti_kivi said:
...
I've been using Sanyos for ... six years? They get replaced after 1-2 years as a matter of course. One set of old 2500s was crap from the start; the present ones (3 sets) - two sets are excellent, one is OK. I tend to top them off on the charger before throwing them in the flash. An ancient 1700 still has a place in my wireless mouse at work

Bret

However, Sanyo 2500 and 2700 seem to develop a very high SD rather quickly/easily. I still have some ancient Radio Shack 1900s that C9000 won't accept and I can only charger them on BC900. However, they still work like you said in a wireless mouse and similar low drain apps (I toss them into toys for kids in case they are lost/forgotten I won't mind their loss). However, they still maintain some charge reasonably well. Meanwhile I have Sanyo 2500s that at some point developed such a high SD that they are truly useless. The ability to develop such a high Sd more than anything else drives me nuts. Meanwhile I have Eneloops that were forgotten some place, down to 0V and still they bounced. Haven't thrown away a single Eneloop yet.

odessit · Feb 18, 2009

I wander how the break-in cycle will influence these cells....
After the SD test I will do a break-in charge followed by another 100 cycles.

bob_ninja · Feb 18, 2009

jtr1962 said:
I'd probably use 80% of initial measured capacity rather than labeled capacity as a criterium for recycling. In that case I get:

Eneloop: 1788/1921 = 93.1%
Sanyo 2700: 2179/2570 = 84.8%

Certainly. As we know too well, labeled/nominal capacity is often far from the actual.

jtr1962 said:
If the capacity continues to decay linearly then the Sanyos will reach 80% ( 2056 mAh) at 191 cycles but the Eneloops will be fine until 1197 cycles.....

Linear decay is highly unlikely at 1A (0.5C/0.4C) discharge rate. Of course testing for 200-300-400 cycles would be too much work so don't expect anyone to do it. So I am just guessing that at some point decay is likely to accelerate. Especially given real life usage is bound to overdischarge cells at some point. It happens.

So I would have a hard time projecting 1000+ cycles for Eneloops given all the perils of real life usage.

bob_ninja · Feb 18, 2009

odessit said:
I wander how the break-in cycle will influence these cells....
After the SD test I will do a break-in charge followed by another 100 cycles.

I would suggest: test SD, break-in and/or refresh-analyze, test SD

Then you could decide to do another 100 cycles, or not.

Sanyo 2700 vs Eneloop - 100 Charge Cycles Analysis

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