New vs Old Eneloops: Constant Current Discharge Performance

[Battery Guy]

Greetings Everyone,

I received my first of the newer 1500x Eneloops last week (purchased here) and ran them through some constant current discharge measurements in order to compare the performance to the older Eneloops.

As always, I spot weld nickel tabs to the cells to minimize contact resistance, and all testing was performed on a Maccor Series 4300 battery tester.

I had hoped that the newer Eneloops would have better high current discharge performance (e.g. less voltage sag), but it looks like they are equivalent or even slightly worse than the older Eneloops.

Here are the discharge curves for 2-10 amp discharge:

So, it appears that there is really nothing particularly great about these new Eneloops except for the reported improvement in cycle life and self discharge rate, both of which require considerable time to test reliably.

Cheers,
BG

 

[Mr Bigglow]

Interesting! So far, I'm glad I bought up some old 'loops sets when they were being sold off cheap! As a matter of interest, how old were the 'old' units tested? Is there a steady decline observed with age as might be guessed at in your graph?

 

[Mr Happy]

Nice graphs :thumbsup:

Are your curves based on testing a single cell, or are they the averaged result of a several cell sample? If the latter, how many cells did you have in each of the New and Old samples?

 

[Battery Guy]

Interesting! So far, I'm glad I bought up some old 'loops sets when they were being sold off cheap! As a matter of interest, how old were the 'old' units tested? Is there a steady decline observed with age as might be guessed at in your graph?

This is the same Eneloop data that I posted in the Eneloop vs Elite 1700 thread, and in the Best Budget LSD thread where I looked at the difference between three year old "Duraloops" and newer (white label Gen 1) Eneloops.

So, just to be clear, the results shown in this thread were not obtained at the same time. I tested these cells within a few days after I received them, but the "Gen 1" white label Eneloops were received about 6 weeks ago, compared to the "Gen 2" blue label Eneloops that I received last week.

Hope this helps to clarify.

Cheers,
BG

 

[Battery Guy]

Nice graphs :thumbsup:

Are your curves based on testing a single cell, or are they the averaged result of a several cell sample? If the latter, how many cells did you have in each of the New and Old samples?

One cell for each, although I have tested other older "Gen 1" white label Eneloops and the results are usually right on top of each other.

I would not make a hard conclusion based on this data since it is only two cells (one of each type), other than there are no significant differences between the two cells. I had hoped to see a big improvement in high rate performance, but unfortunately it does not seem to be there.

Cheers,
BG

 

[InHisName]

I was expecting to give up something to get more cycles out of the life of a cell.

Now since there is a slight diff in high current performance for 'getting' 500 more cycles, If one were to 'get' 500 LESS cycles, then the diff would be GAINED.

If the "X" battery gained by that amount would it join the past 1700 or surpass it in theory ? THAT is probably the eneloop all the current die-hards will be clamoring for in coming weeks.

 

[RepProdigious]

You can discharge eneloops at 10A?!? Even at 1 volt, thats not half bad!

Never thought this was possible.......

 

[Battery Guy]

I was expecting to give up something to get more cycles out of the life of a cell.

Now since there is a slight diff in high current performance for 'getting' 500 more cycles, If one were to 'get' 500 LESS cycles, then the diff would be GAINED.

If the "X" battery gained by that amount would it join the past 1700 or surpass it in theory ? THAT is probably the eneloop all the current die-hards will be clamoring for in coming weeks.

As a general rule, as you add capacity you reduce high current performance. Unless the original 2 Ah Eneloops were under designed, I would expect that the new XX Eneloops with a 2.5 Ah capacity will not perform as well at high current discharges.

For a NiMH cell, you have essentially three design options to increase high current discharge performance: electrode thickness, separator thickness and anode reserve capacity. Here are the trade-offs:

1.) By reducing the electrode thickness, you can get more electrode surface area (more windings), so that the electrode current density (A/cm2) is lower. But by doing this you decrease total capacity because you also need more separator.
2.) By reducing separator thickness, you decrease diffusion distance and increase high current performance, buy you will have higher self discharge and will develop internal short circuits faster. Also, the separator serves as a reservoir for electrolyte, because water is consumed during the discharge reaction and produced during charging. So reducing the thickness of the separator is a pretty tricky game.
3.) By reducing anode reserve capacity, your anode will be thinner, so you get the same benefit as in (1) above, but you won't be able to charge as fast and the cell will be more susceptible to overdischarge damage.

So in order for the new XX 2.5 Ah Eneloops to have the same or better high current performance, Sanyo would have to come up with some material changes, like a higher capacity metal hydride alloy or a new type of separator. It is possible, but I would bet that the new XX cells will not perform as well at high currents as the traditional Eneloops do.

Does anyone know if the XX cells are actually available in Europe yet?

Cheers,
BG