How to charge Eneloops in La Crosse BC-700?

Well I've checked out the other threads but there isn't a general consensus of how to actually charge eneloops.

I just picked up 8 pieces and threw then in my new La Crosse BC-700. I am using the refresh mode so that it discharges and charges it a few times until it detects maximum capacity.

In other threads, people say 0.1C or 0.5C. What does C stand for? I only current in units of Amps or mA...

The BC-700 defaults charging at 200mA. It can also do 500mA and 700mA. It seems like people on the forum like to charge at a higher current? One last question I had was I didn't really understand what you guys mean by termination. How do I know the charger terminated at the right time?

NiMH is at 1.2V right?

Hello Russelljohnson,

Welcome to CPF.

NiMh chemistry is a nominal 1.2 volts. That means that it holds 1.2 volts for most of its discharge. The actual voltage runs from 1.45 volts right off the charger down to 0.9 volts when they are completely discharged. It is pretty much a useless value just like Alkaline cells that are rated at 1.5 volts. Alkaline cells start out at 1.5 volts (or actually a little higher) then drop in voltage from there.

A cell with 2000 mAh of capacity that is subjected to a 2000 mA load will drain the cell in about 1 hour. This is a 1C load. A 0.5C load would drain the cell in 2 hours.

Charging is similar. To charge a 2000 mAh cell at 1C, you would charge at 2000 mA. If you want to charge at 0.5C, you would charge at 1000 mA.

Look up Battery University and you should be able to find a graph on what happens during charging. Basically the cells voltage will continue to rise until the cell is fully charged, then it will drop a little. The charger is set up to recognize this drop in voltage as the time to end or terminate the charge. If the charge continues, the cell can be damaged due to overcharging.

When charging NiMh cells, the strongest termination signal occurs when the cell is charged in the 0.5C - 1.0C range. It is possible to use lower charge rates, but they are not as reliable throughout the life of the cell.

There is a special case when charging at 0.1C. The cell can handle a fair amount of overcharge when charging at this low rate. With a 2000 mAh cell, 0.1C is 200 mA. Since there is not as strong of a termination signal at this low rate, the charge is usually terminated on time. I believe your charger allows you to see how much charge has been put into the cell. If you charge a 2000 mAh cell that is fully discharged and end up putting 3000 mAh back into it, your charger has missed the termination signal and has timed out. The cell has been overcharged.

Tom

Thanks for the clear info Tom.

My charger shows the current mAh of each battery. So to manually know when the battery is finished charging, it should be very close to the rated capacity of 2000mAh correct?

Should I charge at the highest available current from now on? It would only be .35C at the highest. Why do some people say to charge at a lower rate to prolong the battery life? This has got me all confused.

Russelljohnson said:

Should I charge at the highest available current from now on? It would only be .35C at the highest. Why do some people say to charge at a lower rate to prolong the battery life? This has got me all confused.

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There's a lot of debate about this, and there is no absolute certainty about the answer.

This thread of mine might give you some insight. Look at the two charging graphs at 2000 mA and 400 mA. You can see how the dip at the end with 2000 mA is very pronounced (easy for the charger to see), whereas the dip at 400 mA is nearly absent (easy for the charger to miss).

Therefore charging faster makes it easier for the charger to stop when it is supposed to.

Now take a look at this page from Battery University. What is shown on that charging graph and not shown on mine is the internal cell pressure. Notice how the pressure inside the cell goes skywards towards the end of high rate charging, and also how the temperature shoots up steeply.

These changes in pressure and temperature are going to put thermal and mechanical stresses on the cell that over repeated cycles will cause slowly accumulating damage to the internal structures.

Therefore to prolong the life of the cell it would be preferable to use lower charging rates, as long as the charger can detect the end of charge signal and avoid going into over charge. However, in some applications lower charging rates might reduce the ability of the cell to perform at maximum efficiency.

As you can see this is not a simple picture, and there is no perfect answer for every situation. Taking everything together though, the best advice would be to use the 700 mA charge rate for Eneloops on your BC-700.

Thanks Mr. Happy & Tom. Sincerely appreciate the assistance.

Just some personal experience:

I charge my Duracell low discharge cells (like Eneloops) in a LaCrosse BC-9009 at both 200ma and 500ma. They consistently take about 1700-1800maH and terminate perfectly fine. I just charged 2 cells that were showing low in my GPS and each cell took 1790 exactly. Pretty impressive.

How can you manually tell that the battery charge is full? When it's at 1.5V and 2000mAh?

Russelljohnson said:

How can you manually tell that the battery charge is full? When it's at 1.5V and 2000mAh?

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When charging is complete "FULL" will appear on the corresponding slot. The LaCrosse chargers tend to sense end of charge at much lower current than the Maha charger. I routinely use 500 ma rate for my Eneloops.

N162E said:

When charging is complete "FULL" will appear on the corresponding slot. The LaCrosse chargers tend to sense end of charge at much lower current than the Maha charger. I routinely use 500 ma rate for my Eneloops.

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What's the mAh on your full charged cells? One of them have been stuck at 1400mAh for like the past 4 hours. 1.46 volts currently. Is the current mAh reading representative of how much juice is in them?

Russelljohnson said:

What's the mAh on your full charged cells? One of them have been stuck at 1400mAh for like the past 4 hours. 1.46 volts currently. Is the current mAh reading representative of how much juice is in them?

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Fully charged AA sized Eneloops are at 2000mah. If you charged one that has not been fully discharged, then only the amount you used will be put back in, less some waste for inefficiency of the charge process. The current maH reading is how much you have put in the cell, not the capacity of the cell.

guggie said:

Fully charged AA sized Eneloops are at 2000mah. If you charged one that has not been fully discharged, then only the amount you used will be put back in, less some waste for inefficiency of the charge process. The current maH reading is how much you have put in the cell, not the capacity of the cell.

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Hmm... that's weird since I put them on "refresh" which is supposed to discharge them and charge them back up. Wonder if I have bad eneloops.

Russelljohnson said:

Hmm... that's weird since I put them on "refresh" which is supposed to discharge them and charge them back up. Wonder if I have bad eneloops.

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The interpretation of the screen readout depends on the mode you are using. Check your operating manual for your charger.

guggie said:

The interpretation of the screen readout depends on the mode you are using. Check your operating manual for your charger.

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Thanks for tip. Checking the manual once again revealed that the displays have different meanings for different modes. Definitely a good idea to RTFM.

The BC-700, in refresh mode, when displaying capacity:

Shows the capacity discharged while discharging

The capacity of the last discharge while charging,

Then, when finished refreshing, the maximum capacity recorded from the discharge cycles during refresh.

Russelljohnson said:

...One of them have been stuck at 1400mAh for like the past 4 hours. 1.46 volts currently...

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Russelljohnson said:

...that's weird since I put them on "refresh" which is supposed to discharge them and charge them back up. Wonder if I have bad eneloops.

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Reading the manual and understanding how a device works is always a good idea.

Your cell(s) have finished at least one DISCHARGE and the measured CAPACITY was 1400mAh. It's currently in the CHARGE stage, almost complete at 1.46VDC. Healthy Eneloops will terminate at ~1.53VDC on a La Crosse.

The next alphanumeric that you should see on your display will either be 'FULL' or a number greater than 1400. Let's say the next number you see is 1414mAh. It 'beat' 1400mAh, so, it will try again (and again and again), as long as it 'beats' the last number. If the next number is 1400 or less, it will display 'FULL' and stop cycling.

I have a BC-700 question - I did read the manual but am not clear on one point. I am going through my Eneloops and doing the "Discharge/Refresh" cycle on each of them. Some batteries finish ("Full") their cycle ealier. I would like to be able to take those finished cells out and start some new cells on their cycle without interfering with the cells on the charger that had not yet finished. I can't figure out how to program the charger for certain charging bays while not effecting bays that are already in use? Any help is appreciated.

I don't think the charger will let you change modes after a cycle has been selected for a particular cell, so changing the mode or current should only affect the cell you just inserted (within 8 seconds of insertion) and not those that are currently in use. However, I don't have my charger in front of me, so I'm not 100% sure of that.

So, you can ensure single-cell selection only by pressing the compartment key of the cell you insert so that any subsequent mode or current changes only affect that compartment. The compartment key is mentioned on page 6 of the manual, but it doesn't have a clear description of its use.

bltkmt said:

I would like to be able to take those finished cells out and start some new cells on their cycle without interfering with the cells on the charger that had not yet finished. I can't figure out how to program the charger for certain charging bays while not effecting bays that are already in use? Any help is appreciated.

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I think you will need a Maha C9000 to do this. I don't believe the BC-700 has the capability to run independent cycles and modes in each slot.

It works like NutSAK said. You just press the number key for the cell you just inserted, then the display for that cell will start flashing. You can then adjust to whatever mode, current etc. that you desire. The 8 second rule still applies though, and once it commences, you can't change it again without removing the cell and starting over.

Edit: Once you do this, the displays will likely be out of sync. To correct this, you just need to step through the "Display" key to get them all on the same page, so to speak.

Dave

bltkmt said:

I have a BC-700 question - I did read the manual but am not clear on one point. I am going through my Eneloops and doing the "Discharge/Refresh" cycle on each of them. Some batteries finish ("Full") their cycle ealier. I would like to be able to take those finished cells out and start some new cells on their cycle without interfering with the cells on the charger that had not yet finished. I can't figure out how to program the charger for certain charging bays while not effecting bays that are already in use? Any help is appreciated.

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I believe that this post from TTA just a couple days ago covers what you are trying to do. Option 2