AAA - Bad Cell?

[Chase2b]

I have had the C9000 for about a week and was doing a "Refresh/Analyze" on a pair of AAA 900mAh cells for a friend. Don't know how old they are and initial check showed 0.9v & 1.2v. - showing 0 for mAh.
They were then charged/discharged at 200/200.

One cell went through the entire cycle in only 8 hours and on the last charge it was up to 2800mAh at 1.45v.
The second cell never got off the initial charge and 20 hours later was showing 1.45v at 2750 mAh.

For 900 mAh capaacity cells, isn't this (2800 & 2750) high?
Would these cells be considered damaged or trashed?

Note: - the recommended rate by the cell mfg. is = 14-16hrs @ 80ma. Since the C9000 can only go down to a 200ma charge, could this be the reason for THAT much overcharge?

 

[fireguy]

Why not try a break-in and see what happens?

The charge rate of 200 mA for a 900 mAh cell is only 0.22C (22% of capacity), which is less than the C9000's manual states as a minimum 0.33C charge. I believe the newer C9000's recommend an even higher minimum charge rate. I would guess that the battery did not give a voltage drop due to the low charging rate and finally quit because the cell got too hot.

The break-in does a 0.1C charge rate, but it's a special procedure that is timed to stop after 16 hours. Since you don't know the age of the cells they may require a few break-in cycles. This will bring them up to their maximum capacity which may or may not be very good.

As for the initial reading, when the unit begins to charge or discharge a cell, it shows the accumulated mAh which always starts out at 0.

 

[Mr Happy]

Your cells missed termination. This is a common problem with cells in poor condition when using low charge rates. Your reported charge values of about 2800 mAh mean the cells were overcharged, which probably did not do them any good. The charge values should have been closer to 800 mAh.

When charging AAA cells, you should use a minimum charge rate of 400 mA (which is about 0.5 C for most cells).

Also, as fireguy mentioned, if you have cells with no history that might be in very bad condition (or brand new out of the package), you can jump straight to a break-in cycle and do that first. Refresh/analyze is better to use on cells that you already have in use and know something about. A break-in cycle (also callled a conditioning cycle) will bring most cells to a good enough condition for normal charging and further analysis.

 

[Chase2b]

The charge rate of 200 mA for a 900 mAh cell is only 0.22C (22% of capacity), which is less than the C9000's manual states as a minimum 0.33C charge. I believe the newer C9000's recommend an even higher minimum charge rate.
As for the initial reading, when the unit begins to charge or discharge a cell, it shows the accumulated mAh which always starts out at 0.

Thanks, just saw that in the manual. I was always under the impression that 0.1 was the best way to SLOW charge cells, but I quess they meant on "Break-in".
What I meant about the "initial reading" was that the 0# was the mAh reading AFTER the discharge cycle ended.

Your cells missed termination. This is a common problem with cells in poor condition when using low charge rates. Your reported charge values of about 2800 mAh mean the cells were overcharged, which probably did not do them any good. The charge values should have been closer to 800 mAh.

When charging AAA cells, you should use a minimum charge rate of 400 mA (which is about 0.5 C for most cells).

I'll do the 400 mA rate, on the AAA, from now on.
Why does the battery mfg. state using an 80mA rate for 14-16hrs if that's too slow?

 

[Mr Happy]

Thanks, just saw that in the manual. I was always under the impression that 0.1 was the best way to SLOW charge cells, but I quess they meant on "Break-in".
What I meant about the "initial reading" was that the 0# was the mAh reading AFTER the discharge cycle ended.




I'll do the 400 mA rate, on the AAA, from now on.
Why does the battery mfg. state using an 80mA rate for 14-16hrs if that's too slow?

The 80 mA charge for 14-16 hours is a "standard charge". You can access this charge by using the Break-In mode on the C9000.

The standard charge is not too slow because it is 0.1C and because it is run on a timer. The timed charge does not depend on detecting a -dV signal to stop charging, and the batteries are designed so that a 0.1C rate will not harm them if full batteries are charged at this rate for a few hours. The standard charge or Break-In cycle is useful for conditioning batteries for better performance, but is too slow for regular charging.