AA NiMh - Shootout!!

[bbb74]

In this thread: my 2011 shootout between 4 different models of rechargeable AA NiMH batteries. The contenders are:

• 4 x Vapex Instant 2500
• 4 x Eneloop (the newer 1500 cycle ones)
• 4 x Imedion 2400
• 4 x Powerex 2700

The batteries were donated for independent testing by Steve at www.electronicswarehouse.com.au (Vapex & Eneloop) and from Jeff at www.protog.com.au (Imedion and Powerex).


I have a wide range of tests scheduled to test various properties of these batteries, including capacity, variance, self discharge, high load, camera flash cycle times, high cycles, cold temps, and if the memory effect is a myth or not. I will be updating this thread with results as they come in. When I get bored I will do repeated long term self discharge tests (eg 6-12 months).


Notes:

• All charging and capacity checks will be done on a Maha C9000 charger (Model 0J0CA).
• The cells have been labelled VAP1-VAP4, ENE1-ENE4, IME1-IME4, and POW1-POW4.
• In general, VAP1, ENE1, IME1, and POW1 will only be used in slot 1 of the charger, VAP2, ENE2, IME2, and POW2 will only be used in slot 2 of the charger and so on.
• After charging, cells will be left in the C9000 for at least 2 hours after "DONE" appears for the 2 hour 100mA top up charge.

 

[bbb74]

Initial Baseline Results

Ok I now have the initial baseline tests in on all 4 sets of cells.


Out of the packet remaining capacity
Vapex: Average 1,745mAh; Stddev=*168*; Max-min=340mAh
Eneloop: Average 1,370mAh; Stddev=6; Max-min=13mAh
Imedion: Average 1,925 mAh; Stddev=12; Max-min=28mAh
Powerex: Average 281mAh; Stddev=6; Max-min=13mAh


Imedions have the highest capacity out of the packet, followed by vapex and eneloop. It should be noted one of the vapex had an odd result here – 3 cells were similar around the 1660mAh mark, and 1 cell had a capacity about 340mAh higher!?! Using them until flat out of the packet in a 4 cell device could have caused damage from the get-go.

http://www.flickr.com/photos/65263682@N03/5942368957/


Capacity (using breakin cycle)
Vapex: Average 2,331mAh; Stddev=19.6; Max-min=46mAh
Eneloop: Average 1,994mAh; Stddev=7.8; Max-min=17mAh
Imedion: Average 2,278 mAh; Stddev=29.9; Max-min=58mAh
Powerex: Average 2,555mAh; Stddev=13.6; Max-min=29mAh


As percentages: 91% 78% 89% 100%
http://www.flickr.com/photos/65263682@N03/5942368977/


Tests with Canon 430exII full power pops
There is a margin of error with these tests so I'm trying to phrase them in more general terms than the previous test so nothing is too misleading.


A freshly charged eneloop gives faster recycle times than any other cell. The other 3 were behind and roughly in the same ballpark, possibly the powerex were the slowest though and imedion best out of that group of 3.


After a ~500mAh discharge, eneloops were marginally faster than the other cells. The other 3 were pretty similar, but powerex were marginally the slowest again.


After a further ~500mAh discharge, Eneloop, Imedion and Vapex are pretty close (in that order), and the powerex were very slightly behind, maybe.


After a further ~500mAh discharge, Imedion, Powerex, and Vapex were pretty close (in that order) with the eneloops (now getting low in charge) a fair way behind.




Voltage Curves
See this graph:




initial voltage curve



Runtime test in Fenix LD20 torch
Time to drop out of regulation in turbo mode, and relative performance:
Vapex: 117m (89.3%)
Eneloop: 99.5m (76%)
Imedion: 113.6m (86.7%)
Powerex: 131m (100%)
http://www.flickr.com/photos/65263682@N03/5942926214/


Batteries and Torch refrigerated in large cup of cold water at 3 degrees Celsius, and run for 1h 15m. Capacity remaining in cells after this (discharged at 1000mA):
Vapex (average): 694mAh
Eneloop (average): 380mAh
Imedion (average): 719mAh
Powerex (average): 1004mAh




Refresh&Analyse capacity test (+1300mA, -500mA)
Vapex: Average 2,290mAh; Stddev=39.7; Max-min=97mAh
Eneloop: Average 1,931mAh; Stddev=15.6; Max-min=33mAh
Imedion: Average 2,240 mAh; Stddev=26.5; Max-min=54mAh
Powerex: Average 2,503mAh; Stddev=3.7; Max-min=8mAh
http://www.flickr.com/photos/65263682@N03/5942926194/



Any extra conclusions

• The powerex have a significant capacity advantage over the others, they also have the lowest variability in a refresh&analyse cycle, and the 2nd lowest in a breakin cycle. They appear to be slightly slower to recycle my flash, which was honestly a bit of a surprise result given they are popular with photographers.
• Eneloops have the lowest capacity, but the lowest variability in a breakin cycle, and the 2nd lowest in a refresh&analyse cycle. Fresh eneloops cycle a flash the fastest, and maybe a touch faster when more than ~50% charged.
• Imedions have a slightly lower capacity than vapex, but had more charge out of the packet
• Vapex have the 2nd highest capacity and were less variable than the imedions in the first breakin test (3rd place vs 4th place), but switched to being the most variable in the final refresh&analyse test.

All cells are now sitting out for a 1 month self discharge test. That will be followed by a ~1 week self discharge test. Then its either a longer (2 or 3 month) test? Or time to add more cycles??

 

[bbb74]

LSD Results

Results below are for a 31 Day self discharge test (cells were charged and then topped off for 2-3 hours at C/10 rate; discharge after 31 days was the normal 500mA).


Average capacity:
Vapex: 2110 mAh (stddev=40.7mAh; Max-min=98mAh)
Eneloop: 1806 mAh (stddev=12.6mAh; Max-min=28mAh)
Imedion: 2063 mAh (stddev=22.3mAh; Max-min=48mAh)
Powerex: 2291 mAh (stddev=13.2mAh; Max-min=31mAh)


Relative capacities again the powerexs:
Vapex: 92%
Eneloop: 79%
Imedion: 90%
Powerex: 100%


Average mAh "lost" (vs original breakin capacity):
Vapex: 222 mAh (9.5% lost)
Eneloop: 188 mAh (9.4% lost)
Imedion: 215 mAh (9.4% lost)
Powerex: 263 mAh (10.3% lost)


My summary

• Powerex have the highest self discharge but its not bad, and starting out with the highest capacity, easily beat out all the other cells in capacity after 1 month.
• Eneloops have the lowest self discharge, but started out with the lowest original capacity so still came last in capacity by a significant margin
• Eneloops and Powerex had the lowest variation in capacity, followed by Imedion, then vapex

Notes

• Self discharge rates are much higher at the start of a period and slow down with time. I'm doing a 10 day self discharge at the moment. There are various physical mechanisms that cause self discharge, one of them only happens when the cell's voltage is above 1.23 according to Sanyo. So 2 or 3 month test results may show different performance.
• These cells are still very much fresh – results may differ once cells have been used a bit more. That's the next step – going to put a bunch of cycles on the cells and then test self discharge and capacity again. Its going to take some time to get the number of cycles up – going to charge and flatten them repeatedly in a torch.

 

[bbb74]

Other Results

<reserved>

 

[malow]

Re: Other Results

great work! as electronic enthusiast and photographer, your test are 2x useful!

 

[bbb74]

Re: Other Results

Updated baseline results now posted in second post above, for all 4 brands of cells.

 

[samgab]

Re: Other Results

Very interesting tests here. Good work, I'll be interested to see the ongoing results...

 

[ada_potato]

Re: Other Results

Are these all LSD batteries? (Eneloop=LSD) If not, aren't we comparing apples-to-oranges here?

 

[MartinDWhite]

Re: Other Results

It would also be nice to see a test where you tested how much current each batter can put out at given loads. Current output at load is probably why the eneloops charged the flash faster.

 

[bbb74]

Re: Other Results

Are these all LSD batteries? (Eneloop=LSD) If not, aren't we comparing apples-to-oranges here?

I kind of treat "LSD" as being somewhat of a marketing term. 3 of the types in the test are "LSD" but will probably have different self discharge rates. The powerex are not marketed as LSD but they are known to have a pretty low self discharge, which means they'll maintain a higher capacity than eneloops for quite a long time (many many months I believe). So they don't have a "LSD" label on them but they'll effectively beat eneloops in capacity terms for quite some time.

It would also be nice to see a test where you tested how much current each batter can put out at given loads. Current output at load is probably why the eneloops charged the flash faster.

That would be nice but I don't have have something that can do that! Eneloops and Imedions have already been tested like this in previous test on here if you are curious in the results. I'm trying to do real world tests (hence the flash), but yes I'd agree this is why the eneloops were the fastest on the flash test.

 

[beerwax]

Re: Initial Baseline Results

initial voltage curve

if you calculate the available energy from each battery as volts times milliamps (area under the curve) it would appear that an anyloop has similar capacity to the others listed here. a powerex might beat it but the extra bit of capacity is at poor voltage.

cheers

 

[bbb74]

Re: Initial Baseline Results

if you calculate the available energy from each battery as volts times milliamps (area under the curve) it would appear that an anyloop has similar capacity to the others listed here. a powerex might beat it but the extra bit of capacity is at poor voltage.

cheers

Nah I very much doubt that! Otherwise why do all the other batteries have much longer runtimes in torches and flashes etc - pretty close to being proportional to their mAh capacities. Eneloops are simply one of the lowest capacity decent AA NiMhs around.

Also note in the above graph, the minimum scale on the Y-axis is 1.05v. If I did the graph from 0v the difference between the cells would clearly be not that much. The graph effectively "zooms in" on the top part of what would otherwise be much taller columns.

 

[Wrend]

Re: Initial Baseline Results

I would have preferred a little higher resolution than 5 to 6 points. The low V cutoff point seems a little high to me too. I think one of the standard discharge tests is at a 0.2C/h rate down to 1V (or 0.9V) per cell.

Still, I suppose discharging them all at 500mA does give you a "real world" test of sorts. I'm curious how they would compare at 1A or 2A, and how energy loss due to internal resistance would factor in.

 

[bbb74]

Re: Initial Baseline Results

I would have preferred a little higher resolution than 5 to 6 points. The low V cutoff point seems a little high to me too. I think one of the standard discharge tests is at a 0.2C/h rate down to 1V (or 0.9V) per cell.

Still, I suppose discharging them all at 500mA does give you a "real world" test of sorts. I'm curious how they would compare at 1A or 2A, and how energy loss due to internal resistance would factor in.

Sorry I could only be bothered checking every hour, they did go down to 0.9v. The voltage curve was just to get something to compare against once I've put a lot of cycles on the cells to see if there is a change, rather than do a full on voltage curve like I've seen silverfox and others do (with automated equipment).

The runtime test I did in the LD20 would have been around the ~1.3A mark and as you can see, they all held up just fine and lasted a proportional amount to their actual mAh capacities. 1.3A is not hard for any half decent AA NiMh.

 

[Wrend]

Re: Initial Baseline Results

Should have mentioned that I like the way you have them displayed together in the graph for easy comparison, though.

Sorry I could only be bothered checking every hour...

...rather than do a full on voltage curve like I've seen silverfox and others do (with automated equipment).

That's understandable.

One of the tests I did on one of my first sets of 8 Eneloops had me checking the voltage every 15 minutes for over 12 hours straight. Can't say I'd recommend doing that (especially since I never did it again).

http://static.rcgroups.net/forums/attachments/2/7/0/8/7/5/a3143676-72-Eneloop%20T6EX%20Test%20Graph.jpg

 

[InventPeace]

Re: Initial Baseline Results

Whats your conclusion for the "best buy" considering price, capacity, performance, life cycle years of use (LCY), etc. ?

 

[beerwax]

Re: Initial Baseline Results

Nah I very much doubt that! Otherwise why do all the other batteries have much longer runtimes in torches and flashes etc - pretty close to being proportional to their mAh capacities. Eneloops are simply one of the lowest capacity decent AA NiMhs around.

Also note in the above graph, the minimum scale on the Y-axis is 1.05v. If I did the graph from 0v the difference between the cells would clearly be not that much. The graph effectively "zooms in" on the top part of what would otherwise be much taller columns.

yeah i wondered about run times too - they do seem to reflect the milli amp hour capacity of the batteries used. i do observe tho that although i get clearly less runtime with an eneloop in a torch its generally brighter particularly as the runtime progresses. lower voltage in a flash would manifest itself as slower recharge time and you mightnt notice it.
i just raised the issue because i cant recall seeing battery capacity expressed as watt hours , altho im sure it has been , and i thought it might be interesting to see.

even if you extend the y axis to zero you still cant get away from the observation that a chunk of the extra capacity of these higher cap cells is really at low end of the voltage curve, and that the anyloop gives you all the cream that you get from a larger cap cell and that the cream is also sweeter.

be interesting to see the graph from a XXloop

cheers

 

[bbb74]

Re: Initial Baseline Results

Whats your conclusion for the "best buy" considering price, capacity, performance, life cycle years of use (LCY), etc. ?

Well I haven't tested life cycles yet. Where I live the vapex are the cheapest by a fair margin so if they held up with lots of cycles they'd probably be the "best buy". I bought eneloops for my TK41 recently because they were cheaper than the other brands (because they were coming in from overseas with the torch and didn't really cost anything postage wise), and because with 8 cells in the torch I wanted them to not have much variation to avoid reverse charging if I run it flat.

I think it comes down to want you're going to use them for.

yeah i wondered about run times too - they do seem to reflect the milli amp hour capacity of the batteries used. i do observe tho that although i get clearly less runtime with an eneloop in a torch its generally brighter particularly as the runtime progresses. lower voltage in a flash would manifest itself as slower recharge time and you mightnt notice it.

Any decent regulated light is unlikely to be brighter with an eneloop in it - that's the whole point of regulation (and its also why I used a well regulated light for my test ). An unregulated light might be a bit brighter with eneloops (I haven't tested this) but this means it will get flatter even faster.

 

[beerwax]

Re: Initial Baseline Results

Any decent regulated light is unlikely to be brighter with an eneloop in it - that's the whole point of regulation (and its also why I used a well regulated light for my test ). An unregulated light might be a bit brighter with eneloops (I haven't tested this) but this means it will get flatter even faster.

i understand my preon revo to be well regulated. i find it brighter on an eneloop. could be in my head i spose. its a aaa being drained in 50 minutes so its a big load on a tiny battery. i havent noticed it with my aa lights.

cheers

 

[menoceros]

Re: Initial Baseline Results

As to what has been said about the powerex being not completely LSD, thats an understatement. I've been using 2700 Powerex in my cameras fro several yeras and I find that the longest I can leave them is 4 months and then they're practcally dead. Comparing them to enloops or imedions is like comparing a Yugo to a Ferrari. This is why I changed to all LSD batteries in both my lights and my cameras .