Ready to use Rechargeable Battery

eneloop by Sanyo

© Brooke Clarke 2007

Four pack eneloop Ni-MH batteries	Label

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

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

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

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.

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.

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.

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

• eneloop AA Ready-To-Use Ni-MH rated 2000 mAh
• Kodak Ni-MH a couple of years old from my camera.
• Maha Powerex 2700 mAh current production
• Battery Space made in Chine Ni-Cad rated 1800 mAh with tabs (sometimes don't make contact)
  

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).

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?