[ QUOTE ] DDS said:
What would the discharge rate be for a fully charged 18650 cell? Wanted to know how long the cell would stay fully charged. Thanks! Dave
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I don't remember the exact rate but it isn't very much and is even less for a non-protected Li-Ion cell since the protection circuit draws a bit. It's better to store a cell with 40-50% charge or around 3.8V like they come from the factory.
DDS,
I'll tell you, (and what Bill said!) Li-Ion's hold their charge for a LONG time. I'm not a technical guy but Li-Ion's can go weeks, if not months before they start to discharge. I think Bill may be correct as I've put unprotected Li-Ion cells away for weeks and weeks and when I go to charge them, I get the "green" light right away. The protected cells aren't that far away, as with the correct charger, they come around pretty fast.
The only Li-Ion cells that seem to take "forever" to charge for me, are Jon's early R123's but even those charge faster than Ni-MH's. I really like Li-Ion's!
Thanks for the responses guys. I have a SF U2 on the way and I wanted to get the 18650's(protected) for it. I don't know what to expect the run-time to be so I wanted to have batteries ready to go. I bought AW's DSD charger so I presume it will take about 9 hours to charge. I was considering the unproteceted cells but I was informed that a dead short was a potential problem( I'll have to research that problem :-))! Thanks- Dave
I just did a little reading on the subject and here is info of interest:
"The self-discharge of the Li-ion battery is five percent in the first 24 hours after charge and averages 1 to 2 percent per month thereafter. In addition to the natural self-discharge through the chemical cell, the safety circuit draws as much as 3 percent per month. High cycle count and aging has little effect on self-discharge on lithium-based batteries".
They also go on to state that the longevity of a Li-Ion cell is only about 2-3 years even if not used.
It looks like you have found Battery University. It is a great resource. Their information on Li-Ion cells is accurate for the first generation of cells and protection circuits, unfortunately, they have not upgraded this information to reflect improvements that are now available.
Cells are now expected to last 3-4 years due to improvement in the seals, and the protection circuits are drawing less from the cell. The general trend and information is still accurate, but there have been some improvements. As mentioned before, to get the longest storage life from these cells, store them charged to 3.8 volts and in a cool place. The RC hobby people store them in a plastic bag in the refrigerator.
Keep in mind that a cell charged to 3.9 volts (just slightly above the storage recommendation) has just over 50% capacity. This means that you could still get 5 of the 6 levels on the U2, but it would only run about half as long, if your main battery ran out.
Hi Tom: Thanks for the update :-) I actually was reading info about Li-Ion laptop batteries(first google hit). I'm glad to know that there have been improvements. I really plan on using my U2 quite a bit if it is great as everyone states. I wanted to figure out the quantity of batteries to order form AW to keep my U2 up and running strong for continued use. BTW, I know I can search the info out, but what is a dead short? Thanks again for your feedback! Dave
A dead short is when the + and - of the battery get hooked directly together. This can occur due to external influences like damage to the plactic wrapper on the cell, or internal influences like the seperator breaking down.
Thanks Tom! I just ordered some protecetd cells from AW so I presume dead shorts will be less of a concern.
Appreciate the info:-) Dave PS: Can't wait for that U2's arrival!
In my experience, li ion batteries self discharge after a month or two. I have a Canon S100 digicam and carry it with a spare battery in my beltpack. If I freshly charge both batteries and then don't use either one for a while, both go flat. They are good for a few shots but then need to be recharged. It's the same way with my Sony camcorder which I have several batteries for (NP-F550 and NP-F960). It seems to me that the very large NP-F960 pack (which I think has six 18650's inside) is at 50% after 3 months or so. And it's been the same way with any number of cellular phone batteries. After a few months, they power up the phone just fine and show full strength on the battery meter, but go flat fairly fast and need a recharge.
It's possible that some other li ion cells have slower self-discharge, but obviously not all do. So, I'd take the Battery University claims and any manufacturer claims with a grain of salt.
If you're looking to stash a flashlight away and have full strength batteries a year later, use lithium primary cells, not rechargeables.
[ QUOTE ] DDS said:
Thanks for the responses guys. I have a SF U2 on the way and I wanted to get the 18650's(protected) for it. I don't know what to expect the run-time to be so I wanted to have batteries ready to go. I bought AW's DSD charger so I presume it will take about 9 hours to charge. I was considering the unproteceted cells but I was informed that a dead short was a potential problem( I'll have to research that problem :-))! Thanks- Dave
[/ QUOTE ]
I have a SF U2 also and use unprotected 18650 2400mAh cells. The U2 has a built in low volatge cutoff, so unless your worried about shorts or whatever, you can use unprotected cells.
Those 2400mAh cells last forever in the U2 using reduced levels at times. I just love them! [img]/ubbthreads/images/graemlins/grin.gif[/img]
It would seem that there is some draw on your packs causing them to go flat.
My Sony camcorder packs go from 8.34 volts off the charger down to 8.16 volts after 3 months, and these cells are over 2 years old. They have the info-Lithium system in the pack, and it is my understanding that system has a small draw on the power pack to keep the information up to date.
I am not sure what is going on with your cell phone battery...
I don't know if the voltage measurement tells the whole story about how much charge is available in the battery. If you leave your camcorder pack for 3 months and then measure how long it can actually run the camera compared with a freshly charged pack, what happens?
Fully charged, protected 18650,storage duration?
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