Is there a way to check self discharge for AA in a LaCrosse BC900?

[JStraus]

I have some Duracell 2650's that I suspect are self discharging faster than normal. I have had them for a while and have been good batteries.

I have a BC900 and thought I would use the "discharge" mode on a battery after a few weeks of the AA's sitting idle. However I see that the mode will discharge, but then goes to charge mode after that and it does not seem to retain the mA from the discharge cycle once back into the charge cycle. Am I wrong, or is there a better way?
It seems that the batteries, even after 3 weeks idle, when plugged in read about 1.31 V or so. So, I am not sure if by that one is able to tell because I assume that a battery would plateau at around there for quite a while when idle. I am running test cycle to see if their capacity is normal, but I am not sure if this is any indication whether they will hold the charge normally.

Any (good) advice is much appreciated, thanks!

J

 

[shadowjk]

If you cycle through modes until you see both DISCHARGE and REFRESH, it will discharge the batteries, and then begin to charge them again, and repeat multiple times. However, the key thing is that while it is charging, the figure for mAh displayed is the amount discharged from batteries during last discharge. So, set it to DISCHARGE REFRESH, check the charger every 15 minutes or so to see if it has switched to CHARGE REFRESH, if so, cycle through until you get to mAh and write it down. At this point you might want to select the bay that just completed, and change mode to plain CHARGE. Watch out so you don't abort the DISCHARGE REFRESH for the other bays, though

 

[Elliot]

Thanks shadowjk,:thumbsup: I never thought of that and have been using mine for about two years.

 

[Turak]

I have 2 BC900's, love em, and use them regularly. Right next to my 2 MH-C9000's, which are also constantly in use.

Here are a couple methods you can use with the BC900's. Neither are real accurate, but you will be able to tell if the cells are suffering from high self-discharge problems.

Charge the cell until it indicates 'Full' on the BC900.

Then take the cell and set it aside for a week.

Now, put it back into the charger and select 'Discharge' mode.

The problem here is that you have to pay attention to the unit when it starts getting near the end of the discharge (cutoff point is .9V), because it will automatically go into charge mode when it is finished discharging.

Note the mAh discharged. I would note the mAh at 0.91V just to be safe.

The battery should NOT lose more than approximately 10-20% of its total capacity in a 7 day period at normal room temperatures (i.e. 65'F to 75'F.

For example....If it is a 2000 mAh cell and just for giggles, let's say its actual capacity tests out at 2000mAh. Then after you charge it and let it set for a week. Then discharge it, you should get somewhere around 1800mAh.


You could also go the other way....

Charge up a cell till it indicates 'Full'.

Set the cell aside for a week.

Then, put it back in the charger and charge it up till it says 'Full' again. Note the amount of mAh put back into the cell. It will be higher than normal because anywhere from 10-30% of the energy put back in is converted to heat.

For example.....

Again,lets say we have a 2000 mAh cell that actually tests out at 2000mAh

Charge it, set it aside for a week then charge it again.

Now, with this method, I would say that you should see no more than about 20-30% of the energy put back in....which would be about 200-300mAh. If the charger ends up putting a 1000 mAh back in, then that cell lost about 40-50% of its energy due to high self-discharge.

I have a bunch of Energizer 1500's that lose anywhere from 40%-80% within a week. I have seen a couple that lose 75-90% over night.

p.s. I recommend that you do the charging/discharging at the industry recommended rates of .1C charging/.2C discharging or as close to them as possible.

 

[Turbo DV8]

Now, put it back into the charger and select 'Discharge' mode. The problem here is that you have to pay attention to the unit when it starts getting near the end of the discharge (cutoff point is .9V), because it will automatically go into charge mode when it is finished discharging.

If one uses the method shadowjk suggested, the discharge capacity will be retained in the mAh display. Using the discharge function is useless for determining remaining capacity since it erases the discharge capacity as soon as it starts to charge. It's a pet peeve of mine on the BC-700/900's because LaCrosse should have known better... The suggestion to take note of how much current the charger "puts into" the cell gives useless information, for the reasons given in the last post.