Extreme self discharge in new NiMh cells?!

[BatteryCharger]

As I've pointed out before I have quite a pile of NiMh AA batteries. Many of them are Duaracell 2650s. I'm planning on building them into packs, so I've been cycling each battery approximately 3 times, and recording the capacity from my BC700 once they hit at least 2.4ah.

After that I put them in a box and don't pay much attention to them because I've got hundreds of other cells to test. But recently I pulled a few random samples of what I thought were "broken in" batteries, and nearly all of them read 0.9x volts after sitting for between for just 2 weeks and up to 2 months.

OK, I know these aren't LSD cells...but that's HORRIBLE! Is the self discharge higher than usual when the cells are still new and have only been cycled a few times? Or am I doing something else wrong? :thinking:

I haven't been keeping track of the charge dates very closely but I'm going to start now...

(also, many Duraloops charged months earlier and NOT broken in still read 1.32v)

 

[richardcpf]

I used to own a canon 40D camera with a external battery pack and 6 energizer 2500 with it. 3 weeks after a full recharge and no use, they were almost completly depleted! Then I switched to eneloops, the difference was huge.

I also have some sub-C, 7.2v, 1600ma nimh pack for my hobby rc car and they surprisingly does not discharge that bad even after 6 weeks. i believe they will serve better for builing power packs.

My eneloop/duracell white tops reads 1.45 after 10 cycles. I'm using the intelligent duracell charger (the one that has a usb port)

 

[45/70]

Hi BG.

The Duaracell 2650s have been known to do that, as a do a lot of 2000+ mAh cells.

In the quest for maximum capacity, there seems to be a huge trade off in that most of the high cap cells suffer from a high rate of self discharge, sooner or later, sounds like yours were sooner.

Dave

 

[fishinfool]

I've been doing my own nimh self-discharge test on several different kinds of batteries (Eneloops, Powerex 2700's, Energizer 2300's, Duracell 2000's and 2450's, Duraloop 2000 white tops from japan, Rayovac platinum 2100's, Diehard/sears 2000's).

The brand new set of Duracell 2450's which are made in Japan and Diehard 2000's (both bought and broken-in on 5-1-10) were down to 80% when I last tested them on 5-23 with a ZTS MBT-1. I know those 2 aren't lsd's but brand new and broken-in with a 20% loss after only 3 weeks is pretty sad.:thumbsdow

I'll be testing them every week until there is only one left standing.

 

[Lynx_Arc]

that is the main reason many people are either switching to LSD cells (if they even know about the difference) or going to alkalines or lithium primaries. self discharge is more than annoying it is time consuming to charge once a month only to use something for a few hours perhaps using 25% of the capacity up.

 

[BatteryCharger]

Hmmmm. I know the higher capacity batteries have higher self discharge...but what I'm seeing seems absolutely ridiculous to me. (like 2 weeks before they're dead!) I have some older Duracell 2500 batteries in my digital camera and they seem to last about 2 months before they need a charge. I wonder if this is why regular NiMh are actually decreasing in capacity across all brands...

The other thing is they're not ALL behaving that way. Some of my 2650s have been stored for months and they still are in the 1.2v range. Also I have some Energizer 2450s, which have received even less attention from me, but they seem to be keeping their charge for a reasonable amount of time. It's hard to be scientific since I haven't been keeping track of dates...

I wonder if the self discharge will improve with more cycles? Are fresh cells more likely to do this?

I think I'm going to take a random sample of 8 each Duracells, Energizers, and Duraloops, make sure they're cycled and closely matched, and write down the date this time.

 

[VidPro]

Hmmmm. I know the higher capacity batteries have higher self discharge...but what I'm seeing seems absolutely ridiculous to me.

sorta makes all the work on the Rogain graphs making high-caps look wonderfull , end up with all it's hair falling out

from what i have experienced and what others have mentioned, if the high-caps have high self-discharge from the 50 cycles and few years (not new) there is no ammount of cycling that will help them.

in fact , when they are ruined from use (again not new) cycling them they just get worse and worse , relative to how they would get worse from more cycles, and more time.

it was probably one of the most frustrating things to get screwed for $600 (what it costs me) for a rechargable cell item that acts more like a capacitor than a battery. LSD maaaahhhnnn get some, be gone with this misery of bad battery trips After increasing capacity over time, finnally achieving Powirvana, nothing was more depressing to have my hopes squashed , my time wasted by LIES. dont fall for the big numbers.

 

[Bright+]

Good chance you've got a bad batch. I've had a set of 2700mAh (Made in Japan, presumably Sanyo) Sony branded ones that was bundled with the charger that would go flat overnight. All four of them.

 

[fishinfool]

I plan on eventually getting rid of all my non-eneloop/duraloop batteries and having just eneloops. I have family visiting this summer so giving them about 60 aa and aaa rechargeable nimh's should make them very happy. They'll at least be perfect for the kids toys and remote controls.

 

[WildChild]

I have some older Duracell 2650 mAh that weren't much used. While they didn't develop a high self-discharge over time, their internal resistance increased at a point my chargers have a hard time to accept them. I'll just use them one last time until they are discharged and I'll trash them. Duraloop/Eneloop are just to cheap not to replace old crappy cells.

 

[core]

The other thing is they're not ALL behaving that way. Some of my 2650s have been stored for months and they still are in the 1.2v range.

I wonder if the self discharge will improve with more cycles? Are fresh cells more likely to do this?

They almost certainly will not improve with more cycles. Unfortunately they are permanently borked.

As for the difference between your broken-in ones and the ones which have been sitting around thus far unmolested: When you slowly discharge the cell you break down the large crystal formations. (Good, right?) But now that those formations are gone what you are left with is large holes in your wimpy separator. Wimpy by design that is, to get the silly high capacity.

Put a cleaning agent in your old engine's oil and you might have a spotless motor... that now leaks, since the crud is gone that was keeping the seals sealed.

 

[BatteryCharger]

Good chance you've got a bad batch. I've had a set of 2700mAh (Made in Japan, presumably Sanyo) Sony branded ones that was bundled with the charger that would go flat overnight. All four of them.

LOL! I'm at more like 400 Duracells. I didn't pay retail, but if I did, that would be well over $1,000. I'm looking at around a 50% or more failure rate. That is TOTALLY unacceptable!! If these are in fact Sanyo batteries I will no longer consider Sanyo the "be all, end all" battery MFG. Ok, the eneloops are good, but that doesn't excuse this!

I also have several Energizer 2450s that have been sitting untouched since at least December '09, and they mostly all still have some charge. Only a few are down under 1 volt.

As for the difference between your broken-in ones and the ones which have been sitting around thus far unmolested: When you slowly discharge the cell you break down the large crystal formations. (Good, right?) But now that those formations are gone what you are left with is large holes in your wimpy separator. Wimpy by design that is, to get the silly high capacity.

But did I do something wrong to cause this? My procedure has been to charge them as soon as I get them, and I try to recharge at least every 2 months. None have more than 5 cycles on them. From what I've read on the date codes on the batteries, it seems they can already be a year or more old when you buy them...

While we're talking about it, does a full self discharge down to 0.9v or less "count" as a cycle as far as battery capacity and life are concerned, the same way as if you used it in a flashlight or something?

 

[TakeTheActive]

...But did I do something wrong to cause this? My procedure has been to charge them as soon as I get them, and I try to recharge at least every 2 months. None have more than 5 cycles on them... From what I've read on the date codes on the batteries, it seems they can already be a year or more old when you buy them...

1. Buy only as many cells as you're going to use (i.e. "Use 'em or Lose 'em").
2. Charge cells just before you're going to use them.
3. Store cells @ ~25% charge in a cool place.
4. Refresh & Analyze non-LSD unused cells once every 30 days.

...does a full self discharge down to 0.9v or less "count" as a cycle as far as battery capacity and life are concerned, the same way as if you used it in a flashlight or something?

Why shouldn't it? :thinking:

 

[illumiGeek]

That's been my experience with high cap AA batteries as well. Some will go a while before they act up, but all will fail with high self discharge before you have gotten any significant use out of them (a dozen cycles if you are lucky).

They are all crap. I loathe the day that LSD cell makers start ramping up capacity since they will inevitably ruin them as well.

 

[Egsise]

LOL! I'm at more like 400 Duracells. I didn't pay retail, but if I did, that would be well over $1,000. I'm looking at around a 50% or more failure rate. That is TOTALLY unacceptable!! If these are in fact Sanyo batteries I will no longer consider Sanyo the "be all, end all" battery MFG. Ok, the eneloops are good, but that doesn't excuse this!

Interesting, are you unsatisfied to Duracell or Sanyo?

I have Sony 2700 cells that have the squarish button and they go flat in a week or two.

 

[Russel]

...After that I put them in a box and don't pay much attention to them because I've got hundreds of other cells to test. But recently I pulled a few random samples of what I thought were "broken in" batteries, and nearly all of them read 0.9x volts after sitting for between for just 2 weeks and up to 2 months.

OK, I know these aren't LSD cells...but that's HORRIBLE! Is the self discharge higher than usual when the cells are still new and have only been cycled a few times? Or am I doing something else wrong? :thinking:

A couple decades ago I tried NiMH rechargabe AA cells only to find that they would be completely depleted, without being used, in one week. I found that very frustrating. But that is characteristic of non LSD batteries.

...(also, many Duraloops charged months earlier and NOT broken in still read 1.32v)

That is the true beauty of low self discharge NiMH cells. They are fantastic in this regard.

 

[BatteryCharger]

1. Buy only as many cells as you're going to use (i.e. "Use 'em or Lose 'em").
2. Charge cells just before you're going to use them.

1. 
   Don't even get me started on that! :duh2: It was mostly a deal I couldn't pass up, and generally turned out to be a bad idea. I always expect to charge regular NiMh before I use them, but all the other batteries I've had in the past could do at least a month.
   
   I have some ~10 year old Duracell 1800mah batteries that still perform decently without excessive self discharge. I have totally abused these batteries, forgot about them for years, even reverse charged a few of them!

 

[BatteryCharger]

Interesting, are you unsatisfied to Duracell or Sanyo?

Well, I don't know it as a fact, but all the evidence I've been able to find points to Sanyo as the OEM. If that's true then Sanyo batteries just plain suck. They tend to have a good reputation but I'm wondering if they deserve it.

I can't really blame Duracell because they don't ever make their own rechargeables...

 

[Mr Happy]

But did I do something wrong to cause this? My procedure has been to charge them as soon as I get them, and I try to recharge at least every 2 months.

Yes, possibly you did. In traditional NiMH cells, the process of self-discharge from a fully charged state causes internal degradation of the cell, leading to irreversible deterioration over time. The golden rule with both NiCd cells and traditional NiMH cells is never store them in a charged state. With NiCd cells it is best to store them at 0 V, with NiMH store them at 1.2 V. In both cases it is best to store them in a refrigerator since low temperatures slow down chemical reactions.

Going through a cycle of letting them discharge by themselves and then repeatedly charging them up again is a very bad maintenance strategy, almost the worst maintenance strategy possible.

The best maintenance strategy for cells not in regular use is to store them discharged, then put them through a manual charge/discharge cycle every few months before storing them discharged again.

(This does not apply to LSD cells, which can be stored charged or discharged at your choice. Since they have low self-discharge, they do not suffer the self-discharge damage that regular cells suffer.)

 

[TakeTheActive]

...I have some ~10 year old Duracell 1800mah batteries that still perform decently without excessive self discharge. I have totally abused these batteries, forgot about them for years, even reverse charged a few of them!

Thicker separator.

I have MANY old non-LSD (ABUSED by *CRAP* chargers) Rayovac NiMH cells (1300mAh, 1600mAh) in rotation that hold 'some' charge for months (90 day rotation in clocks, thermometers, remotes).

IMO, purchasing 'High Capacity' non-LSD NiMH cells was your first mistake and charging them before you needed them was your second. You live and you learn - I've certainly made MY share of mistakes!