Ready to use Rechargeable Battery

eneloop by Sanyo

© Brooke Clarke 2007

eneloop Four pack
Lable on eneloop Batteries
Four pack eneloop Ni-MH batteries
Label

Background
    Sanyo eneloop AA
    Duracell
    Rayovac AAA
Internal Resistance
Shelf Life Testing
    Preliminary Capacity Table
    Test Results Table

Background

Although rechargeable batteries like the Ni-Cad and Ni-MH, can be more economical than primary types they have a high self discharge rate.  For example if you place a fully charged Ni-MH battery on the shelf and come back in a couple of months to use it, the battery will be about dead.  This is very different from Alkaline or Lithium primary cells that can sit on the shelf for years and still deliver full capacity.

Comparison of common rechargeable chemistries for shelf life (Self discharge).

Chemistry
% / month
Ni-MH
30
Ni-Cad
15 to 20
Li-xx
2 to 3
Ready to Use Ni-MH
1.5
Lead Acid
1.4

I think another problem is that if a Ni-MH is left for a few months on the shelf it will not take a full charge on the first try, but instead needs to be formed, broken-in or cycled depending on what name you put on it.  Most people don't have that capability and so the battery goes into the round filing cabinet.  If these batteries really hold a charge as claimed (90% at 6 months, 85% at one year) then they are much more practical for users that are not constantly using them.

There are a number of companies offering these Ni-MH cells with "Pre Charged" or "Low Discharge" or "Low Self Discharge" in the title.  Also note they don't prominently display the capacity like is done on competitive Ni-MH cells. 

A 1927 Franco No. 1041 three AA size Pocket Flash Light battery has a guarentee on the back saying it will not drgrade more than 10% per month.

The No. 6 Dry Cell (Zinc Carbon) when tested six months after manufacture had degraded by:
Year
% / 6 mo
% / mo
1901
35
6.9
1916
25
4.7
1934
7
1.2
1951
2
0.3
Specification for Dry Cells and Batteries by Sectional Committee on Dry Cells and Batteries - C18, NBS 1954
%/mo Calculation example:
35 % means remaining charge is 0.65 which equals X ^(fraction per month)
0.65^(1/6) = 0.930720
1 - 0.930720 = 0.06928 which is 6.9 %/mo

Sanyo eneloop

These Sanyo eneloop AA cells are labeled as Ni-MH with a capacity of 2 Ah (1.9 AH minimum).  The hot Ni-MH cells are now around 2.9 AH, so you give up a little capacity to get the long shelf life.  But if these are as good as they are cracked up to be then they will have more capacity than a 2.9 Ah cell after both sit on the shelf for a month or so.

Upon opening the package I charged them on the Maha MH-C777Plus and they took about 0.3 AH, so if their capacity is 2 Ah they were  15 % discharged.  The date code is 2006 05 (May 2006) and it's now mid Oct 2007 or 15 months later.  A normal Ni-MH would be completely dead by now.

Next test is to discharge in the Maha MH-C777Plus to get some idea of the capacity of a series string of 4 cells. 
After 81 minutes the C777 reports only 470 mAh at 4.1 volts.  I think the 777+ did not properly charge them.

There's a problem with the C777Plus and eneloop cells.  It will NOT discharge them and instead charges for awhile then quits.

23 Oct 2007 - The C777Plus beeps for 5 seconds after the discharge is complete and displays the data.  Then automatically after 15 minutes it switches to charge mode and charges the battery then beeps some more.  If you miss the first beep you miss the discharge data.   I'm running the eneloops again.  At 141 minutes into the discharge there has been 841 mAh delivered.

The plan is to do a few charge overnight -> discharge the next day cycles to see how repeatable they are.  If that shows some predictability then some shelf time can be added into the mix.  Some Powerizer (China) and Kodak Ni-MH cells as well as some no brand Ni-Cad cells can be run in parallel for comparison.

Duracell

Duracell will be offering a blister pack of 4 AA cells Fall 2007 (but I don't see any web presence (5 Nov 07).

Rayovac AAA

The back of the package has a graphic that shows 80% charge after 9 months for the "Hybrid" and 40% after 6 months for conventional rechargables.  The packaging looks Canadian, i.e. everything is done twice, once in English and again in French.
Rayovac Ready To Use AAA batteries 4 pack
Rayovac Ready To Use AAA batteries 4 pack
Rayovac Ready To Use AAA batteries 4 pack

Got these cells to replace the bad cells in a couple of Solar Garden Lights.   I think the low self discharge will be especially helpful for this application where the cells are being used to less that full capacity for during the winder months.

I have 2 cells on discharge measurement, two at 100 ma and two at 200 ma to see how much of the 800 mHa label capacity they have.
ID
A1
A2
A3
A4
B1
B2
B3
B4
Capacity as received
6441
5951
6192
6212
6072
405
6092
412
6122
408
6082
406
Capacity at
different rates
7823
260 min
7713
259 min
7364
122 min
7824
130 min
na
na
na
na
Capacity after
Break-in 5
797
782
770
800
785
326
771
322
775
320
774
323
Working       mAh
Capaacity6     min




785
524
766
517
780
518
786
524
Note 1 discharged at 200 ma
Note 2 discharged at 100 ma
Note 3 mAh Determined by charging on Maha MH-C401FS and measuring capacity on Maha C9000 at 200 ma.
Note 4 mAh Determined by charging on Maha MH-C401FS and measuring capacity on Maha C9000 at 400 ma.
Note 5 mAh based on C9000 charging, not ture capacity using C401FS charger. discharge at 100 ma
Note 6 Working capacity based on Slow MH-C401FS charge & 100 ma C9000 discharge.

11 Jan 2008 -Rayovac Hybrid AAA cells 2B, 3B and 4B have been charged in the C401FS and are going into the square solar garden light.

The three NEXcell batteries have been removed from the round solar garden light and are being capacity tested at 100 ma.
Rayovac cells A1, A2 and A4 are going into the round solar garden light.
A dab of Lube-Gel applied to both ends of each cell just prior to installing, then the cell rotated in place.
The capacity test of the NEXcell batteries removed from the working round solar garden light are very interesting.  Two of the cells are showing ZERO capacity done testing at 0 minutes and 1.26 volts, i.e. they could not supply 100 ma.  But the thrid cell when done shows 37 minutes, 55 mAh 1.24 volts.  Note 100 ma is the lowest discharge rate the Maha C9000 can be set to but the LEDs in the solar garden light will make light with a few ma.  That idea combined with the 1.26 Volts says the cells are not dead but just don't have enough capacity to supply 100 ma.  They probably can supply 10 ma.
It will be interesting to see if using fresh low sheld cells show any difference in performance.

Kodak Pre-Charged

Walmart photo section also carries Kodak Digital Camera Battery, package of 4 AA cells, UPC 4177181988, KAARPC-4, CAT 181 9887
20 Feb 2008 - put in my digital camera.

Internal Resistance

Although the spec sheet says 25 milli ohms they measure 0.00 to 0.01 Ohms, i.e. zero to 10 milli ohms on my ESR tester.

Shelf Life Testing

What's a good, easy way to do this?  Tying up a computer and some line powered test equipment for a battery capacity test that takes 24 hours is easy, but a shelf life test that's going to run for many months is something else.

Amp Hours Capacity

3 Nov 2007 1 pm - Four Ready To Use batteries are on the MH-C9000 going thuough the Break-in cycle that ends with the batteries charged.  Just finished Breaking-In four Maha 2700 mAh Powerizer batteries and they were about 1.4 Volts during charge.  The RTU batteries are at 1.50 Volts during charge.  This process takes about 24 hours.
4 Nov 2007 about noon - Break-In fininshed.

Maha Reference cells came out:


1
2
3
4
Tmin
9
10
9
8
Volts now
1.2
1.2
1.2
1.2
mAh
128
133
137
126

eneloop


1
2
3
4
Tmin 106
110
113
109
Volts now 1.44
1.45
1.44
1.44
mAh 1607
1660
1709
1650

 Ni-Cad reference cells came out:


1
2
3
4
Tmin
170
166
169
165
Volts now
1.41
1.41
1.41
1.41
mAh
1284
1242
1276
1238

Kodak


na
na
na
na
Tmin
273
316
281
315
Volts now
1.41
1.43
1.40
1.43
mAh
1317
1508
1359
1511
7 Nov 2007 - Four diffeent battery brands have been refreshed.  Next the capacity will be measured, where instead of loading the C9000 with the same type of battery one each of the different types will be loaded.  This way the difference in test times will be more like some number of seconds instaead of a day or two.

Preliminary Discharge Test

The C9000 is in the Discharge mode where it will not do any charging, just measure the cell capacity.
The idea is to measure the discharge capacity to see how it compares to the values above, i.e. does it repeat.
started 7 Nov 2007 about noon

1
2
3
4
Brand
Sanyo
Maha
China
Kodak
C mAh
2000
2700
1800
1600
Discharge
200
200
200
200
10pm 7nov07   Capacity B#1
1798
1816
1247
1460
10am 8 Nov07    Capacity B#2? 1927
2131

1715
10am 9Nov07   DisCap B#2 1759
2419
1194
1414
1am 11Nov07    DisCap B#3 1743
2414
1187
1204
Capacity B#4 1720
2382
1128
1217
10 nov starting discharge of battery #3 about noon.
11 Nov took off batt #3 after charging 200 ma & put batt #4 on for discharge.
12 Nov 02 9 am - read batt#4 and put B#4 on 200 ma charge. 

Preliminary Capacity Table

The idea here is to get a feel for how repeatable the data is.  This will be the basis for the shelf life test interval.

Batteries Under Test

The batteries are identified by a letter number combination:
eneloop = e1, e2, e3, e4   Powerex=P1, P2, P3, P4, Kodak = K1, K2, K3, K4,  China = C1, C2, C3, C4
mAh
e1
e2
e3
e4
P1
P2
P3
P4
K1
K2
K3
K4
C1
C2
C3
C4

NiM
NiM NiM NiM NiM NiM NiM NiM NiM NiM NiM NiM NiC
NiC NiC NiC
Rating
2000
2000 2000 2000 2700
2700 2700 2700 1600
1600 1600 1600 1800
1800 1800 1800
Note 1
1607
1660
1709
1650
2597
2588
2595
2607
1317
1508
1359
1511
1284
1282
1276
1238
7-12Nov07 1798
1927
1743
1720
1816
2419
2414
2382
1460
1715
1204
1217
na
1194
1187
1128
13-18 Nov07
1923
1802
1793
1783
2541
2398
2375
2381
1414
1349
1175
1194
1331
1221
1213
err3
18 -20Nov07
1848
1812
1831
1827
2395
19493
2427
2440
1329
1340
1192
1209
1216
1224
err3
1274
20-23Nov074
1898
1838
1854
1853
2444
2421
2449
2463
1346
1371
1182
1212
1271
1228
err
1243
23-
1889
1849
1850
1838
2454
2428
2448
2453
1316
1360
1174
1204
err
1217
1218
1220
Average (last 2)
1894
1844
1852
1845
2449
2425
2449
2458
1331
1366
1178
1208
1271
1223
1218
1232
R
9
11
4
15
10
3
1
5
15
6
4
4
na
11
na
12
Note 1 - first capacities are after the break in process which uses a different charging profile than this test.
Note 2 - starting with batt #3 17Nov07 the charging will be on the MH-C401FS and discharging stays on the C9000.  This should (1) speed things up and (2) provide more consistant charging.
Note 3 Maybe the tabs are not making good contact and the C9000 sees a new cell and charges it.  Twice I'm positive I put it into discharge mode, but later it has charged the cell. Human error, i.e. if you put a cell in the C9000 and do nothing it will charge it.  So i'ts best to put in one cell and do all the setup for that cell, not put in all four at once.
Note 4 -23 Nov 2007 - After using the C401-FS for charging the results are getting much more repeatable.  With the exception of an obivious blunder at 18 Nov on the P2 cell all of them are repeating to much better than 1% (i.e. the first 2 digits are the same, and in some cases repeating to 3 digits 0.1%).  Also see the 401FS page on Consistency.  When discharging the C9000 is sitting on top of my computer which is under the table (desk).  The computer is on 24/7 and has 5 fans, one of which blows warm air out the top.  So the discharge is being done in a crudely temperature controlled environment.  It's 60 to 65 deg F range.

The repeatability seems to be typically better than 1%.  The eneloop may loose just under 2% after one month but the Ni-MH and Ni-Cad might loose that much in a day or two.  So measuring every 4 weeks (not a month) looks like a good interval.  Starting 23 Nov
Discharge is at 500 ma.  Charge in C401FS.

Test Results Table

Date
Weeks
mAh e
mAh P
mAh K
mAh C
21 Dec 2007 e1, P1, K1, C1
4
1761
93%
2253
92%
1169
88%
1050
83%
18 Jan 2008 e2, P2, K2, C2 8
1694
92%
2158
89%
1161
85%
970
79%
15 Feb 2008 e3, P3, K3, C3 12
1667
90%
2112
86%
784
67% 2
921
76%
14 Mar 2008 e4, P4, K4, C4 16
1646
89%
2087
85%
990
82%
848
69%
9 May 2008 e1, P1, K1, C1 201
1698
89%
2048
84%
1066
80%
847
67%
6 June 2008 e2, P2, K2, C2 24
-3-
-3- -3- -3-
4 July 2008 e3, P3, K3, C3 28
-3- -3- -3- -3-
1 Aug 2008 e4, P4, K4, C4 32
-3- -3- -3- -3-
26 Sep 2008 e2, P2, K2, C2
-something wrong this date-
40
718
39%
494
20%
718
53%
457
38%
12 Nov 2008 -4- e3, P3, K3, C3
46.5
1581
85%
1739
71%
0
dead
361
30%
21 Nov 2008
48




Note 1 - after testing the 4 cells are charged and put back on the shelf.  For example after testing Batt#1 on 21 Dec (it's been on the shelf 4 weeks) it's charged and 20 weeks after 21 Dec tested again on 9 May 2008.  That's why the gap of 8 weeks between 14 March and 9 May.  If this continues the gaps will keep getting longer since there are only 4 cells of each type.
Note 2 - 14 March after taking the data on K4 today that data taken on K3 15 Feb looks like it's lower than it should be.  We'll see in the next round.
The Maha Powerex 2700 mAh so far is the clear winner in terms of mAh available.  
9 May 2008 - asked Maha about Powerex 2700 vs their Imedion 2100 and the answer is capacity vs. cost.
A four pack of Imedion 2100 is $14 (1.5 mHh/¢)  vs. a four pack of Powerex 2700 for $17 (1.6 mHh/¢)
Note -3- Missed these dates so moving to 26 Sep 2008 (next 4 week time slot since today is 7 Sep).
Note -4- Missed the 4 week mark by a week and a half, sorry personal distraction
13 Nov 2008 - adding four Imedion 2100 mAh AA cells to replace the Kodak 1600 mAh cells.
17 Nov 2008 - adding four Powerex 2700 mAh cells since these seem to be the highest performing cells (strange that they arrived almost dead).

I1
I2
I3
I4
P5
P6
P7
P8
500 ma disC. (as received) na
na
na
na
41
49 49
41
Break-In 2099
2122
2070
2142
2541
2570 2562
2617
500 ma disC.
2104
2134
2091
2160
2532
2550
2547
2607
C401 chg -> 500 ma disC.
2033
2137
2097
2101
2474
2500
2494
2552
C401 chg -> 500 ma disC. 2071
2116
2107
2121
2480
2493
2489
2544
C401 chg -> 500 ma disC. 2063
2135
2060
2160
2486
2507
2497
2552
15 Dec = 4 weeks  I1

x
x
x
x
x
x
x
20 Dec = 4 weeks
x
x
x
x

x
x
x

Capacity Loss Due To Inactivity

If a Ni-MH or Ni-Cad battery is put on the shelf for a long time, not only does it loose charge but also it looses capacity to be charged.  For example a pack of Ni-MH cells might provide 2000 mAh when discharged.  But after sitting on the shelf for 2 years after one charge can only provide 50 mAh.  So has temporarily lost 1950 mAh of capacity.  If the pack is charge discharge cycled many times it will regain some but not all of it's capacity.  There is the temporary and the permanent capacity loss.

Many people will toss a battery if it does not take a charge on the first try.  But it can take many cycles to reform the battery.
21 Dec 2007 - Observation The Maha 2700 Powerex are sold as ordinary Ni-MH but seem to also be long shelf life.  They are within 1 % (repeatability of test) of the eneloops.   The recent data sheet for the 2700AA Powerex cells has the same format as the Sanyo data sheets, maybe Sanyo made the Powerex cells?

Links

Sanyo - Batteries09/13/2006 Press Release -
SANYO research shows that Eneloop batteries have an 85 per cent residual ratio after one year of non-use in 20 degree Celsius temperatures (compared to regular rechargeables that lose one per cent of power per day), meaning the batteries can be left in an electronic device for months, but the batteries will retain 85 per cent of their charge. Internal tests also prove that Eneloop batteries can take 4.4 times more digital pictures than dry cell batteries, even in zero degree Celsius conditions. Eneloop maintains its low self-discharge rate and stability in temperatures as low as minus 5 degrees Celsius.

Duracell Precharged - no specs
Powerizer Imedion - 2.1 AH

Back to Brooke's PRC68, Alphabetical web page list,   Products for Sale, Batteries, Battery Chargers, Battery Patents, Battery Test, Military Information, Personal Home

page created Oct 18, 2007.