New AW 18650 2900's fully charged, at rest voltage

I just recently got some new AW protected 18650 for the Fenix TK35. I have charged them with an Icharger 208B at .80 A to 4.20 voltage. Before I can even take them off of the charger the voltage reads 4.18v and I checked this with two different Fluke DMM's. After 5 minutes of resting time, I checked them again with Both Flukes and I get 4.155 with one of them and 4.157 with the other. After 15 minutes of resting time all the batteries are between 4.13v and 4.135v with the same meter. I only used one of the Flukes the last time but checked all 6 batteries and even hooked them back up to the Icharger and went to the monitor screen to confirm that the voltage is 4.13v on the Icharger. It seems that both of my meters and the Icharger are all reading close to the same voltage.

Does this seem normal for the AW 2900's?

I have some green unprotected 18650's salvaged out of an old laptop battery that will remain at 4.18v after 2 weeks from fully charged. I was a afraid to use the unprotected 18650's in the TK35, that's why I purchased the the AW protected 2900's. Did I make a mistake in purchasing the AW's? After searching on here it seems like I got some old cells. I have not cycled them to measure the capacity yet, maybe tomorrow. How much capacity am I loosing and should I be concerned?

I purchased 6 of the 18650's and 4 of 17670's, new from a reputable seller at the Marketplace. I have only charged one of the 17670's, but the results are very similar. Any info. would be greatly appreciated before I contact the seller as a disappointed customer.

Hi One. That does seem a bit low for new cells. Usually, new cells settle down to 4.18-4.19 Volts after a short rest. I charge all my Li-Ion cells (including LiFe and LiMn) at a 0.5C rate. One question. Were you using "charge", or "fast charge"? Fast charge will yield similar results to what your getting, with new LiCo cells, as it doesn't charge the cells to quite the same level, with the 0.2C cutoff.

Dave

My 4 AW 2900's always come off my Pila at 4.14 and settle at 4.12. Never worried about it because I know this will increase the life span of them.

45/70, Thanks for the reply.

I was using the regular "charge" mode. I have not used the "fast charge" mode on the charger yet, its new to me also and I am slowly learning all of its features. Doesn't it seem odd that out of 10 new batteries the 7 that I have tried are all the same. If I didn't have the salvaged 18650's that do read 4.20v fresh of the charger and 4.18v 2 weeks later, I would think that the charger and my meters are reading low.

Would a .5c rate on the AW 2900's be 1.45A? Am I charging these at to low of a rate? I have been charging the the 18650's at .80A

I don't want to contact the seller until I am sure there is something wrong with the cells. Should I be concerned with that much of a voltage drop? Like I stated earlier, the charger is showing 18v before I can get them unhooked from the charger. It's not like they are being charged unattended, I am only 10-15' away tinkering on another project and just waiting for the charger to start beeping, indicating that they are done.

Onebadengine said:

Doesn't it seem odd that out of 10 new batteries the 7 that I have tried are all the same.

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If they're all the same that's good, it indicates consistency. If they were all different it would be more worrying. It seems you have discovered what is normal for those cells. I don't have any to tell you about, but on the surface 4.13 V does not seem that bad. It might be a little lower than unprotected cells because of the protection circuit.

gearhead1972 said:

My 4 AW 2900's always come off my Pila at 4.14 and settle at 4.12. Never worried about it because I know this will increase the life span of them.

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Gearhead, I am not sure that is the same, it would be different I was stopping the charge at a lower voltage and trying to prolong battery life. I am not really shooting for max. life expectancy but rather max. capacity. I know that my batteries are at 4.20v while on the charger (checked with a Fluke meter to confirm what the charger is already telling me) I am willing to accept that by charging them to the max., that it will shorten there life, but its hard to accept that their life/capacity has already been reduced and it has nothing to do with me and my charging habits.

Mr Happy said:

If they're all the same that's good, it indicates consistency. If they were all different it would be more worrying. It seems you have discovered what is normal for those cells. I don't have any to tell you about, but on the surface 4.13 V does not seem that bad. It might be a little lower than unprotected cells because of the protection circuit.

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You know that, I never looked at it like that. Maybe I am being all anal over nothing, but at the price of these things it nice to be sure. I don't mind spending a little more on a good product, but, hate spending more only to find out that the product is not so good.

After everything that I have read on here and on the net, it seems like these batteries have a bigger sag in voltage, compared to what others have posted.

Do a capacity discharge test and see what you get. This will tell you how the battery will perform.

Onebadengine said:

I know that my batteries are at 4.20v while on the charger (checked with a Fluke meter to confirm what the charger is already telling me)

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When the batteries are being charged the batteries are not at 4.20 V, the charger is at 4.20 V. The batteries are less than 4.20 V by an amount corresponding to the charge current. For the batteries to reach 4.20 V you would have to leave them on the charger forever until the current dropped to zero. Since the charger stops before the charge current reaches zero the voltage of the batteries is always less than 4.20 V when they come off the charger. How much less is a characteristic of individual batteries and some kinds of battery are slightly different than other kinds.

When you have a brand new battery you should record the voltage obtained when it comes off the charger and make that your "as new" benchmark for that cell. As the cell ages the voltage off the charger will decrease, and by comparing to the as new benchmark you can get an indication of the age and health of the cell.

The slower you charge the more complete the charge will be. That's because your charge terminates at 1/10'th the starting charge rate. A lower termination current will get you a more complete charge. I usually charge everything at 500mah unless I'm in a rush. On my AW's, charging at 500mah, which means a 50mah termination current usually makes them settle in at 4.15 or 4.16 volts.

I normally charges my 18650 at about 1.5 A (icharger). That does not give them full charge before termination. If I want full charge. I top up the batteries by restarting the charging at a lower rate. The I can get very close to 4.2 V. Another important factor is to connect the balancing leads, and if I charge more than one cell I use balancing charge.

I've wondered why the icharger can't have a custom termination current. Would be awfully nice if you could just set a 1.5 amp charge and a 50 mah termination current.

infinus said:

I've wondered why the icharger can't have a custom termination current. Would be awfully nice if you could just set a 1.5 amp charge and a 50 mah termination current.

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The longer a Li-Ion cell spends in the CV stage, the more damaging it is to the cell. This is because at the higher voltages near charge termination, the electrodes of the cell are more easily oxidized. This is also why the CC/CV algorithm is used. The declining current level during the CV stage lessons the damage to the cell, as the voltage rises towards the end of charge. This is also why chargers that use a CC only, or an approximation of a CC/CV algorithm, incorporating a "pulse" charge, are damaging to Li-Ion cells.

As for the C/10 used by hobby chargers, this is mostly a compromise between relatively fast charging, capacity, and cell longevity. Most Li-Ion cells can be reasonably charged with a C/30 termination. Much below that, damage to the cells becomes a problem. Some of the new high capacity cells however, utilize a termination rate lower than C/30. This is at least in part, how these cells obtain the higher capacity.

The bottom line though, is you generally do not want a termination rate below about C/30 for most Li-Ion cells. If a C/10, or better yet, a C/5 termination is used, the cells will last considerably longer, with only marginally less capacity.

Dave

I don't think that the choice of C/10 or C/30 termination is really about damage to the cell, as such. It is more about security and reliability of termination. If you consider for example an old cell with a voltage that quickly falls to 4.0 V when removed from the charger, such a cell might have a charge current that never falls below C/30 in the CV stage, no matter how long you leave it on charge. This of course would be dangerous since it might mean a missed termination and an indefinite trickle charge. So I think the reason for C/10 is to guarantee that charging will terminate in a defined manner.

If you are an expert user who owns a voltmeter and carefully monitors your cells, then you can use a C/30 or even a C/50 termination setting. But since many people are buying and using lithium ion cells without ever owning a voltmeter or measuring their cells at all, then using C/10 seems to be a safe choice for the average user. (If you are an expert user with an iCharger, then you can of course top up your cells after the main charge at 1.5 A by programming a second charge at 0.5 A.)

45/70 said:

The bottom line though, is you generally do not want a termination rate below about C/30 for most Li-Ion cells. If a C/10, or better yet, a C/5 termination is used, the cells will last considerably longer, with only marginally less capacity.

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Do you have any data to back this up? I don't think this information is quite accurate. Otherwise, why would companies such as Sanyo and Panasonic, recommend ~C/50 termination for their 18650 cells? Even in their cycle life tests 300-500 cycles, this is all done at ~C/50 termination with 50-60mA or so depending in the cell.

Using higher termination currents like C/10, C/5 etc, would result in some-what of an "incomplete" charge cycle. I would guess that C/10 or C/5 may increase cycle life by 5-10% or so, because the cell would likely come off the charger at a lower voltage of 4.1-4.15 or so.

Mr H, Jason, this page on Battery University makes several references to cell health vs. termination of charge.

jasonck08 said:

Do you have any data to back this up? I don't think this information is quite accurate.

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In addition, Jason , I believe the high cap cells you refer to have the additional nickel layer added to the anode (LiNiCo). This layer helps reduce oxidation of the electrode, along with generally making the cell safer, both during charge and discharge. With typical LiCo Li-Ion cells however, this does not apply.

Dave

jasonck08 said:

I would guess that C/10 or C/5 may increase cycle life by 5-10% or so, because the cell would likely come off the charger at a lower voltage of 4.1-4.15 or so.

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Actually, not quite. Cycle life is exponentially related to charge voltage, so charging to 4.1 V will give a very much greater cycle life than charging to 4.2 V. Not 5-10% but maybe 5 or 10 times more cycles.

Hi Mr Happy, So are you saying that when you charge up a laptop, that A person could gain 5 to 10 times more battery life by charging it to only say 90% and unpluging the charger. Just try to see if this does apply. I do Know there a pack of cells but would this increase the life of the laptop pack. It seems it would. I just never really thought of it until now.

45/70 said:

Mr H, Jason, this page on Battery University makes several references to cell health vs. termination of charge.

In addition, Jason , I believe the high cap cells you refer to have the additional nickel layer added to the anode (LiNiCo). This layer helps reduce oxidation of the electrode, along with generally making the cell safer, both during charge and discharge. With typical LiCo Li-Ion cells however, this does not apply.

Dave

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I frequently check battery university, but the page you referenced does not mention that an increase in termination current will result in "considerably longer" cycle life.
And no, I was not referring to any specific size or capacity of cells, I was simply pointing out my observations. Take a look at any of the LiCo datasheets from Sanyo. All of them that I have opened up show a recommended ~C/50 termination. Most of Panasonic's cells are also like this (with the exception of some of the higher power cells with lower IR having a higher cutoff).

Mr Happy said:

Actually, not quite. Cycle life is exponentially related to charge voltage, so charging to 4.1 V will give a very much greater cycle life than charging to 4.2 V. Not 5-10% but maybe 5 or 10 times more cycles.

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5-10x, I don't believe that for a second. Otherwise, why wouldn't more companies release cells spec'ed with a 4.1v charge voltage and advertise 3000-4000 cycles. I'm pretty sure most people would be willing to take a 10-15% capacity hit if they could get 5-10x out of their cells.

I remember reading that military long life Li-ion cells are only charged to a max of 3.92v to extend cycle life. There was no mention though how much it actually does increase cycle life...

jasonck08 said:

5-10x, I don't believe that for a second. Otherwise, why wouldn't more companies release cells spec'ed with a 4.1v charge voltage and advertise 3000-4000 cycles. I'm pretty sure most people would be willing to take a 10-15% capacity hit if they could get 5-10x out of their cells.

I remember reading that military long life Li-ion cells are only charged to a max of 3.92v to extend cycle life. There was no mention though how much it actually does increase cycle life...

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Fair enough, maybe not 5-10x. On a quick search I did find that charging to 3.92 V is estimated to double the service life.