Is final voltage important after a charge?

[fireguy]

Hello again!

In my quest for battery knowledge, I have come up with yet another question!

After charging a battery, how important is the final voltage shown for the cell? I just completed a break-in on two AA NiMH cells using a C9000 and notice quite a different voltage being reported.

The first is a new 2400 mAh battery (chinese one) which has gone through a break-in cycle four times. It's showing 1903 mAh which is only 79% of rated capacity. It was originally 1818, then 1834 and 1863. It has increased marginally each time. I would have thought it should be much higher after these cycles, so I'm thinking the cell is poor quality. The final voltage was 1.40V.

A second (Ultra Pro) cell was purchased 3 years ago. It never went through a forming charge and has probably been used and recharged about 6 times. It sat for about 2 years but is in good physical condition. I didn't think to measure the voltage, but I did a break-in and the rating was 1727 / 2500 (69%) and the voltage was 1.25V.

What should the final charge on a healthy AA NiMH cell be? Is the end voltage as important as the reported capacity in mAh?

Thanks again for all the great education!

:wave:

 

[mdocod]

There will be variances in termination voltage depending on the charge rate selected. Around 1.4-1.5V is pretty normal.

 

[fireguy]

Thank you. I will have to do a break-in then and see if that cell ends up closer to 1.4 V. I guess I have to watch both the end mAh and the voltage then, when trying to decide if a cell is ok.

 

[mdocod]

an end-voltage of ~1.25V does suggest something strange if you ask me... cell is probably on it's way out, but I'd be tempted to exercise it a bit and see how it does..

Problem with nickel chemistry cells, is they really need to be exercised on a somewhat regular basis to stay healthy. That cell that was left sitting un-used for several years may or may not recover, more than likely not. Large crystal formations in the electrolyte can get so out of hand, that they literally start to puncture the separator materials within the cell. This, in essence, is like thousands of little microscopic internal shorts, once this type of damage is done, it is irreversible. Significant voltage suppression is one of the major side effects of large crystal growth, so that's what my money is on right now. Exercising the cells (cycling them) on at least a somewhat routine basis is actually much more healthy for them than just letting them sit un-used.

Eric

 

[fireguy]

an end-voltage of ~1.25V does suggest something strange if you ask me... cell is probably on it's way out, but I'd be tempted to exercise it a bit and see how it does..

Problem with nickel chemistry cells, is they really need to be exercised on a somewhat regular basis to stay healthy. That cell that was left sitting un-used for several years may or may not recover, more than likely not. Large crystal formations in the electrolyte can get so out of hand, that they literally start to puncture the separator materials within the cell. This, in essence, is like thousands of little microscopic internal shorts, once this type of damage is done, it is irreversible. Significant voltage suppression is one of the major side effects of large crystal growth, so that's what my money is on right now. Exercising the cells (cycling them) on at least a somewhat routine basis is actually much more healthy for them than just letting them sit un-used.

Eric

Many thanks for your reply. I really appreciate everyone who takes the time to answer stoopid newbie questions! :twothumbs

Your explanation makes sense. I will do a couple of break-in cycles and see how they perform. They weren't expensive batteries, so I'll chalk it up to education. Too bad it takes so long to do this. I really need another C9000! They should sell them in pairs.

Unfortunately, I had all but forgotten about these batteries. I know that I bought 4, but can only find 2 of them. They do look like disposable batteries, so I think someone took them out of a cordless mouse or something similar and tossed them. After I found those two I went on a hunt... Found 3 Ray-O-Vac 2500 NiMh (not hybrids) in a toy that hadn't been used for 6 months. I put one on a break-in to see what condition it's in. Strangely, I can't even remember buying these ones. I'm sure they were charged once when new, put into the toy and then forgotten. I'm guessing they're about a year old. And I wonder what happened to #4 as well. Forgive me, it was before I became a battery geek. I promise I won't let good cells sit until they're no longer good.

As for the cheap chinese ones, that too was a purchase made before I found CPF. The manufacturer says they will ship me new ones and test the ones I have to see why they are crap. I'm guessing that the new ones may yield the same results, but it will be interesting to see what the do send.

 

[fireguy]

Many thanks for your reply. I really appreciate everyone who takes the time to answer stoopid newbie questions! :twothumbs

Your explanation makes sense. I will do a couple of break-in cycles and see how they perform. They weren't expensive batteries, so I'll chalk it up to education. Too bad it takes so long to do this. I really need another C9000! They should sell them in pairs.

Unfortunately, I had all but forgotten about these batteries. I know that I bought 4, but can only find 2 of them. They do look like disposable batteries, so I think someone took them out of a cordless mouse or something similar and tossed them. After I found those two I went on a hunt... Found 3 Ray-O-Vac 2500 NiMh (not hybrids) in a toy that hadn't been used for 6 months. I put one on a break-in to see what condition it's in. Strangely, I can't even remember buying these ones. I'm sure they were charged once when new, put into the toy and then forgotten. I'm guessing they're about a year old. And I wonder what happened to #4 as well. Forgive me, it was before I became a battery geek. I promise I won't let good cells sit until they're no longer good.

As for the cheap chinese ones, that too was a purchase made before I found CPF. The manufacturer says they will ship me new ones and test the ones I have to see why they are crap. I'm guessing that the new ones may yield the same results, but it will be interesting to see what the do send.

Edit: Update: I finished the break-in on the Ray-O-Vac 2500 NiMh. After being charged once, being infrequently used for several months then sitting idle for 6 months, the break-in charge showed a capacity of 2324 mAh or 93% of the rated capacity. That's a pretty impressive cell, IMHO.