When to replace an AA NiMH battery?

[digifish]

Greetings, I just purchased a Maha C9000, I should have purchased 2

I saw mentioned in the C9000 support thread that a battery that can't reach 0.8 C, after repeated attempts to refresh/condition it is ready for the bin.

What is the general consensus, what do you retire your NiMH AA's at? My wife has kindly donated the corner of her laundry as a battery-lab

Thanks digifish

 

[SilverFox]

Hello Digifish,

Welcome to CPF.

There are two general outlooks on when to replace cells...

Cycle testing is usually done down to 60% of initial capacity, however it does not address voltage under load. I replace my cells when they fall to 80% of their initial capacity. At 80% there still is some life left in them, for low drain applications, however I feel they are well on their way to becoming "crap" cells.

I expect my cells to remain vibrant and to be strong performers. Recycling them at 80% of their initial capacity does a good job of meeting my expectations.

Tom

 

[digifish]

Hello Digifish,

Cycle testing is usually done down to 60% of initial capacity, however it does not address voltage under load. ...

I expect my cells to remain vibrant and to be strong performers. Recycling them at 80% of their initial capacity does a good job of meeting my expectations.

Tom

Thanks Tom,

nice place to be, I use a lot of AA rechargable batteries in portable audio recording equipment and can't have my gear going down in the middle of a recording session. I am not all that obsessed about economy, I just want to know my batteries are full, in a good state of tune and ready to rumble.

Your comment on the cycle testing wasn't clear to me. I understand you can cycle batteries and at some point they will reach their maximum potential then start to degrade (assuming they will benefit from refreshing/cycling). I am not sure what the 60% is about in that context?

Using a C9000 I assume that the 80% rule would be the mAh rating of the battery * 0.8 compared to the reading after a 'break-in' or 'refresh' cycle?

Regards Scott

 

[Mitch470]

Hello Digifish,

Welcome to CPF.

There are two general outlooks on when to replace cells...

Cycle testing is usually done down to 60% of initial capacity, however it does not address voltage under load. I replace my cells when they fall to 80% of their initial capacity. At 80% there still is some life left in them, for low drain applications, however I feel they are well on their way to becoming "crap" cells.

I expect my cells to remain vibrant and to be strong performers. Recycling them at 80% of their initial capacity does a good job of meeting my expectations.

Tom

Tom,

What do you mean by "capacity?" Do you mean Voltage or Discharge Capacity? I can measure voltage with my Radio Shack Multimeter or my LaCrosse BC-900. I can measure Relative Voltage as a function of 5 LED's with my DigiCam Battery Tester. However, to measure Discharge Capacity, I must use my LaCrosse BC-900 and run a full Charge/Discharge/Charge in Test Mode. I am using Eneloop Batteries.

I notice that the Test Mode Full Cycle takes my Eneloop rechargeable batteries down to .9V and then up to 1.52V. They settle at 1.38V after being out of the charger overnight and reach the 5 LED's. Non-rechargeable Energizer Lithiums start with 1.75V and 5 LED's. Eneloops start with 2000 mAh and the Energizer Lithiums start with 3000 mAh.

Does running Test Mode Full Cycles to test "Capacity" wear out the Eneloop batteries? They are rated at 1,000 Cycles so giving up 500 Cycles to run tests would still not be material to me since I doubt I would run more than 10 Instrument Use Cycles per year on each battery in any event. After 2 years I am sure I will be replacing all due to the appearance of better batteries on the market by that time.

I do not use regular Alkalines since the cost difference between them and Lithiums is too small to be relevant for me considering my total level of use each year.

I have heard that Isotope Batteries with unlimited life will be out in the next 3 years in any event. Maybe they will prove unpopular due to a slight cancer risk in using them.

 

[saildude]

I use the "Refresh Analyze" mode when checking the health of cells - one caution - you will get a bit different results based on your charge and discharge rates. Use consistent test rates - if you have good cells they should last a long time - the C-9000 stops the discharge when it meets the low voltage limit - I have some cells that are several years old and still fine - have some others that had a real high self-discharge rate ( went flat just sitting on the shelf ) that have been pitched.

There should be some threads on the C-9000 charger - batteries and the best or not so good charge and discharge rates.

mb

 

[digifish]

I use the "Refresh Analyze" mode when checking the health of cells - one caution - you will get a bit different results based on your charge and discharge rates.

Yes I was just about to ask about that. It seems to me that if the fate of your battery hangs in the balance then the break-in mode should be used to make the decision?

Regards Scott

 

[SilverFox]

Hello Scott,

There are standards used in battery testing. The standard for determining the number of cycles a battery is good for, specifies that the cell will be charged and discharged until it falls below 60% of its initial capacity. This is how the battery manufacturers come up with a cycle life of 500 or 1000 cycles.

Please note that a battery re-labeler seems to be allowed to state anything they want to concerning capacity and cycle life, but the battery manufacturers usually follow the standards and test cells from each manufacturing batch.

This is all good and well, however, as a cell ages it developes higher internal resistance. This causes a higher voltage drop under load. The cycle standard test allows for testing a lower current draws than you may be using in your application. This means that your results would be different than the standard test results.

I have found that by only using the cells until they drop to 80% of their initial capacity, I avoid issues brought on by the cell developing higher internal resistance.

Tom

 

[SilverFox]

Hello Mitch,

Capacity refers to mAh or Ah of the cell, or battery. This is determined by multiplying the time a cell or battery can hold up to a load by the load.

For example, if you subject a cell to a 400 milliamp load and it holds the load for 5 hours before the voltage drops below 1.0 volts, this cell has a capacity of 2000 mAh.

In direct drive lights, higher voltage under load will result in a brighter light. If the light is regulated, this difference is not noticeable until the light falls out of regulation.

Yes, batteries are only good for a limited amount of cycles. Test cycles use up cycle life. In general, it is good to run a complete discharge cycle every 25 - 50 shallow charge/discharge cycles. If you push your cells to the limit and beyond, you may need to do a complete discharge more often.

Tom

 

[VidPro]

To the original OP question:
i keep mine till they are a pain in the buttox, then one day when i am in a Toss 'em mood, out they go.
if they serve the function by which they were designed, and are less trouble than they, and the money are worth, then something can use them.
its not like they leak (often) or blow up, or fuse, or cause major problem.

What you dont know cant hurt you, till they dont do what you want them too.
meaning when we didnt have all these gadgets to know the actual capacity to the percent, we just used them till they didnt do what we wanted.

 

[TorchBoy]

i keep mine till they are a pain in the buttox, then one day when i am in a Toss 'em mood, out they go.

Same here, except I give mine to friends who typically have even worse cells.

meaning when we didnt have all these gadgets to know the actual capacity to the percent, we just used them till they didnt do what we wanted.

Actually, it was the original MH-C9000 which fried most of my AAA cells, before that they weren't great but they worked fine. :mecry: The friends' dumb slow chargers still get the most out of them, and I got an updated MH-C9000 for my new cells. :laughing:

 

[digifish]

Thanks Silverfox.

Vidpro & TorchBoy sensible...too sensible, how am I supposed to feed my battery habit...I love rechargables! Any excuse to buy a new set

Regards Scott

 

[Mitch470]

Hello Mitch,

Capacity refers to mAh or Ah of the cell, or battery. This is determined by multiplying the time a cell or battery can hold up to a load by the load.

For example, if you subject a cell to a 400 milliamp load and it holds the load for 5 hours before the voltage drops below 1.0 volts, this cell has a capacity of 2000 mAh.

In direct drive lights, higher voltage under load will result in a brighter light. If the light is regulated, this difference is not noticeable until the light falls out of regulation.

Yes, batteries are only good for a limited amount of cycles. Test cycles use up cycle life. In general, it is good to run a complete discharge cycle every 25 - 50 shallow charge/discharge cycles. If you push your cells to the limit and beyond, you may need to do a complete discharge more often.

Tom

Tom,

Since it isn't practical to count the cycles for each cell, I am going to just do a Test Mode Charge (charge/discharge/charge) with the BC-900 once per year on all of the Eneloops. If any in storage drop under 40% capacity (2 LED's out of 5 on the Digicam Tester), then I will also do a Test Mode Charge at that time. I'll check them all with the Digicam once per month.

When I place them into use, I will just do a simple Charge Mode Charge to top them off.

 

[cave dave]

Its a good idea to do a self discharge test too. Charge em up and let them sit for two weeks then do a dischahrge for capacity. If they have less than 50% after 2 weeks toss em.

 

[etc]

How do you check the capacity?
I have a multimeter.

>I replace my cells when they fall to 80% of their initial capacity

 

[TorchBoy]

How do you check the capacity?
I have a multimeter.

If you can't borrow a MH-C9000 or other capacity-testing device (eg, BC-900) then connect your multimeter to the cell to measure its voltage and short the cell's terminals with (say) a 3 ohm, 5 watt resistor. Measure the time taken for the cell to drop to 1.0V. Do a bit of calculating and integrate to get capacity (or plot a graph and find the area under the graph). Could be fun.