Rechargable battery question

Hi all. Some of you are very knowledgeable about rechargeable batteries, so even though I hate starting a new topic for this, I have to ask.

I have a Lacrosse BC900U charger, and several sets of eneloops.

One set of AAA eneloops has been giving my a problem. I put them in my Harmony Remote, fully charged, and within a day the remote is dying. I have another set, and the remote normally runs 4 to 5 weeks with that set. I have the multiple sets clearly marked, so I don't mix them up.

Anyway, after having this happen a few times, I decided to do a refresh on that set with the Lacrosse. It ran several days, and here are the final results.

16    |   16   |  16    |   17 mA
1.50  |  1.50  |  1.50  | 1.49 V
739   | 804    |  822   |  840 mAh

What are the numbers you provided? They look like the numbers you would see while the batteries are being charged, which does not tell you much about the battery except that 739-840 is a lot to put into those batteries. How do the numbers compare with your good set of batteries?

Is the ma the the ammount trickling into the cells when you looked at the display?
Is the voltage the voltage of the cells being charged?
Is the mah the amount of charge put into the battery during that charge cycle?

I speculate one low capacity cell in the 'bad set'. Run that set on the remote until the remote is dying, then pull the set and check voltage on each cell in the set...a bad cell will become apparent.

Thanks.

The numbers I listed are the readings from the Lacrosse BC900U after the full refresh cycle completed.

I'll have to read the manual (ugh) to see if I can just use it to get a reading on the batteries after some use. I don't recall if there is a mode that doesn't automatically start charging or discharging the batteries.

As Wilt said. Check the batteries when they are dead or under a load. It is hard to tell much from a charged battery. Just like a bad car battery shows good voltage until you put a load on it and the voltage plumets (leaving you to walk home in the rain).

I assume you will see different numbers on your charger depending on when you look. My chargers (I use mostly LiPoly's) will beep when "charged" but actually the beep or fully charged indication comes when the batteries are at about 95%. So if I look soon after is says charged it sill indicates a current flow into the batteries (charging) then over the next half hour the current flowing into the batteries will drop to near zero. My chargers record the amount of charge put into the battery so a bad cell will take only 250mAh to go from discharged to charged while a good one will take 750mAh. Judging by the price of the Lacrosse BC900U I am not sure if it actually records the amount of current put into batteries. It may put a number on the display but I'm not sure it has an accurate way of determining the number.

In the refresh mode that I used earlier, it repeatedly discharges and recharges the batteries (individually) until
no further increase in the measured capacities is estimated.

The final readings I listed before were as follows:

(V) Instantaneous Battery Voltage
(mA) Trickle charging curret
(mAh) Maximum battery capacity determined in discharging
(T) Elapsed time of last discharging -- I didn't record this reading


The charger also has a test mode, which will fully charge each battery, then discharge to determine capacity, and then fully charge again.

Will this be useful in helping me determine which battery is faulty?

It would appear that battery 1 has 9-12% less capacity compared to other batteries. But that itself is not a clear cut indicatory of 'guilty' sentence. You mentioned four factors but only listed three...the T value would seem to be the indicator you need.

Wilt wrote in post #7219799
You mentioned four factors but only listed three...the T value would seem to be the indicator you need.

I know. When I first looked over the details of what the final readings meant, I mis-read the (T) result as time elapsed charging, rather than time elapsed discharging.

The one thing that should be immediately helpful is that the voltage reading is instantaneous, so a significant difference after some use should be immediately evident.

You have one set that works well in the remote and one set that does not. How do the numbers from your charger differ? If there is such an obvious difference in their performance the chargers numbers should clearly show it.

Luckily I have 2 extra AAA eneloops.

Anyway, after running that set in the remote for almost 2 days, it was starting to die again. I put the set back in the Lacrosse BC900 to check the voltages, and the #1 battery was showing 'null' which indicates a damaged battery. The other 3 batteries were all showing voltages around 1.35.

So, the #1 battery is out, being replaced with one of the spares.