When is a cell done?

Im wondering if there is a chart of some sort to determine when a battery(s) life is done with ?
I'm using a Maha MC-C9000 to analyze some of my battery's . What point should the be considered dead?
example
battery rated for 2250 mAh and after a refresh/analyze Im getting 2028 mAh

Thanks for any info I have searched and wasn't able to find anything relevant
lovecpf

The general recommendation that I hear often is that when it's below 80% of its original usable capacity, then it's getting pretty close to recycling time. It's a slipperier slope from there on out.

But what it really comes down to is if it still provides a useful function for you or not.

battery rated for 2250 mAh and after a refresh/analyze Im getting 2028 mAh

Click to expand...

Batteries are often rather optimistically rated, so this one specifically probably isn't too far gone yet.

Hello Flugpop,

Welcome to CPF.

A general indication that a cell has gone from vibrant to crap is when its capacity drops below 80% of its initial capacity, when it no longer holds a decent voltage under load, and when its self discharge rate increases. With that said keep in mind that some people prefer to use crap cells in less demanding applications.

Tom

Yes, that's a good point too. You'll also want the cell to be able to properly maintain a high enough discharge rate and voltage level for the application that you're using it in for it to still be useful.

From what I've read here, the MH-C9000 will often reject older worn out cells. So that too might be a good indicator that they're on their way out.

I was a little surprised by the state of some of the cells people were trying to recover on the MH-C9000, and that even spent alkaline cells where performing better.

A cell is done when the difference between OCV and CCV is at its maximum.

If the C9000 is reading "HIGH", the cell is done. It not worth the effort to keep the cell going since the high internal resistance will create a lot of heat during charge and cause a large voltage drop during discharge.


If the C9000 is showing an ICV, I will use the following formula (based on Ohm's law) for calculating internal resistance:

Mikl1984 said:

ICV itself isn't sufficient
More interesting to evaluate Ri by Maha data ONLY

Recently one russian guy found rather good evaluation formulа http://forum.ixbt.com/topic.cgi?id=20:28873-17#483

Final formulа is
Ri=(ICV-V2-0.09V)/1.97A

V2 - second voltage value after ICV
1.97A - current during less than 10 sec after Charge begin
http://forum.ixbt.com/topic.cgi?id=20:24112:4652#4652

Real difference between ICV from Maha and DMM about 0.11V
0.09V is empirical based on increasing V2 till it shows

Evaluating this way Ri is corresponding with values from iCharger, for example

Click to expand...

It takes less than 15 seconds to get the ICV and V2:

1. Insert just 1 battery into an empty slot on the Maha C9000
2. Hit "Enter" twice (this will start a 1000 mAh charge)
3. Write down the first voltage display (this is the ICV)
4. Write down the second voltage display (this is the V2)
5. Use the Ri=(ICV-V2-0.09V)/1.97A formula to get battery Internal Resistance in Ohm


Let use a new eneloop AA cell for example:

After inserting the cell in the C9000 and hit Enter twice, the first voltage displayed (ICV) is 1.56V. The display then cycle through capacity, current, time then voltage again. The second voltage displayed (V2) is 1.37V. The V2 is alway lower than ICV. Now we can use the formula:

Ri= (1.56V - 1.37V - 0.09V) / 1.97A = 0.051 Ohm or 51mΩ

New and fresh battery has a IR around 50mΩ. The half-life point is between 100-200mΩ. Battery is getting near retirement time as it reach 300mΩ. Anything over 300mΩ is a goner.


Internal Resistance is only one factor for determine battery life. The second important factor is the remaining capacity. Most manufactures recommend replacing battery when the capacity drops below 80% of its initial capacity. This is not alway the case since the battery may still be useful in low drain device (remote, mice). 80% of a 1900 mAh eneloop AA is still 1520 mAh. This is 50% higher capacity than the eneloop lite that Sanyo recommend for low drain device.
So you got a eneloop "hi-lite" version once your eneloop reach a 80% capacity

In summary, the cell is done when the internal resistance is too high and the remaining capacity is too low to make it useful in your application. The Maha C9000 can help you determine the two importance factors to make your decision.

ecrbattery said:

If the C9000 is showing an ICV, I will use the following formula (based on Ohm's law) for calculating internal resistance:

Click to expand...

You guys are loosing me a bit on the correction value for the second C9000 voltage reading, I see 0.09, 0.11, and 0.12 Volt referenced. I understand why a correction value is being implemented, as the cell has already started charging when the reading is taken, but am unclear as to why there are three values mentioned?

Also, I looked at the link Mikl posted, and I must admit that my Russian is very, very poor. :candle: I took two years of Russian about 40 years ago (in high school), but at the same time, became more interested in girls and motorcycles (or was it motorcycles and girls?:thinking. Anyway, a very interesting method for determining cell health, and I might add that both you guy's English is way better than my Russian!

Dave

Thanks for all the wonderful information lots to take in lol but I do get the basics. Maybe this can be a sticky ?

Dave, your poor Russian is a lot better than mine. Google Chrome browser does a pretty nice job of translating the Russian thread. A lot of good technical info there on both the Maha C9000 and the LaCrosse chargers.

The 0.09V correction value is for contact resistance on the C9000.

Now that there is a way to determine IR with the C9000, it is up to all the C9000 owners to get some data for reference.

ecrbattery said:

...
If the C9000 is showing an ICV, I will use the following formula (based on Ohm's law) for calculating internal resistance:
...

Click to expand...

Very interesting. Has this been confirmed to be an accurate measurement by anyone else? (That is, not just a measurement of relative IR.)

Most cell manufacturers consider their cells "end of life" when they deliver less than 70-80% of the original capacity.

ecrbattery said:

The 0.09V correction value is for contact resistance on the C9000.

Click to expand...

Ah, I see. OK, so it would seem to me there should also be some correction factor in the formula to compensate for the fact that when the second voltage sampling is taken, the cell has been charging for 15 seconds. This has to raise the voltage of the cell some small amount, compared to when the first voltage sampling is taken, no? Maybe the difference is so small, it wouldn't really matter.

Dave, your poor Russian is a lot better than mine. Google Chrome browser does a pretty nice job of translating the Russian thread.

Click to expand...

Yeah, I thought about using a translator, but I don't use Google Chrome and I thought I'd give it a try anyway. I got the gist of most of it, but mostly because I "reverse engineered" from each side of the stated figures, to see if I could see what they were talking about.

Dave

When you stick a fork in it. :naughty:

Sorry could not resist, back to your regular scheduled program. :devil: