Normal discharge for non LSD NiMh?

[Art]

Hi,
I recently bought a "smart charger" with a 1000mah charge capability , its actually very nice but I only start using it last week. Before this I had a cheap one that had a max of 150mah charge... it would take nearly 1day to charge a 2700mah AA battery and only in pairs.
So before this I measured the voltage in my Duracells Supreme 1000mah AAA and after one day of charge they are ate 1,380v and after one week ate 1,370v more less. This I had already tested with the cheap charger.
With this new one its the same but my new AA Duracells 2650mah seem to be a bit worse.

Charged one AA yesterday and they end up always ate 1,420v... today I measured 1,380v.. that seems normal but a pair of 2 that I charged 1 week ago are at 1,305 now... a bit low compared to the AAA 1000mah that keep more than 1,35v for 1 month. :thinking:

Is this normal? Is it probably because they are still new and the AAA have already some break in done?

Please post your discharge experiences specially with eneloops that I dont have them here.

Regards

 

[Marduke]

Typical non-LSD cells will discharge at about 1% per day. When they are nearing the end of their lives, it can be much greater than that. Energizer 2500's could somehow manage more than 10% per day.

All NiMH cells after charging will have a period of higher initial self discharge. Eneloops for example, this will last for a few weeks. After that, the discharge goes remarkably flat, and you end up with 85% initial capacity after 12 months.

 

[SilverFox]

Hello Art,

With NiMh chemistry, open circuit voltage is not a reliable method of determining the state of charge of a cell. There are even some issues with trying to determine the state of charge using a loaded voltage reading. The best way is to do a discharge test and then you know for sure.

In the first post of this thread, there is a graph showing the percentage of remaining capacity you can expect after a period of self discharge based on various self discharge rates. As Marduke mentioned, the advertised self discharge rate for NiMh is 1% of the remaining capacity per day. Better quality cells seem to fall into the 0.7% range, but that can be rounded up to 1% to include a broader range of cells.

You will notice that the Eneloop self discharge rate is a lot lower than the other rates. I should add that this graph is based on short term observations, which are then projected to longer term results. The self discharge rate does not remain constant, so these results are a little pessimistic.

Tom

 

[Art]

The relation between voltage and its capacity is that different?
This charger has a discharge function but it does not give you the battery mah capacity it only discharges it.
So reading the voltage is no good for this test?

The AAA that is always in my pocket in a L0D read 1,275v and I already used it for 1month since last charge and I use it ate least 2 or 3minutes every day (average).
This cell has had like 5 cycles and seems to be very good in self discharging and keep its power since its a 1000mah.
I also have here some uniross AA 1600mah LSDs... but I havent tested them yet.

Regards

 

[SilverFox]

Hello Art,

The problem seems to be that there isn't much spread in voltage between a full cell and an empty cell.

You are talking about a cell that is now showing 1.275 volts, and it started out at around 1.35 volts. I have empty cells that read 1.252 volts. This means that our range from full to empty sees a voltage change of only 0.098 volts. There is enough variation in cells to wipe out a good portion of that difference, so now it is coming down to having a very repeatable and accurate voltmeter and very consistent methods of taking readings, along with cells that are all in similar condition.

Tom

 

[Art]

Hello Art,

The problem seems to be that there isn't much spread in voltage between a full cell and an empty cell.

You are talking about a cell that is now showing 1.275 volts, and it started out at around 1.35 volts. I have empty cells that read 1.252 volts. This means that our range from full to empty sees a voltage change of only 0.098 volts. There is enough variation in cells to wipe out a good portion of that difference, so now it is coming down to having a very repeatable and accurate voltmeter and very consistent methods of taking readings, along with cells that are all in similar condition.

Tom

Yes , I just tested more cells and I have here 2 1700mah AA Duracells with already some use.
They red 1,25volts but as soons as I put them on a small discharge rate of 500mah took like 5min for them to get to 0,9v :thinking:

Seems like read voltage is not really the best way... but still the AAA Supreme Duracells are the ones getting less voltage drop in time.

Will try to post some data I have here later today

Regards,