18650 Battery - Questions

[HEDP]

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So I just bought an Ultrafire Charger and three AW 18650 batteries at the advice of people on this board. (Really surprised how small the 18650's are, I thought they'd be Streamlight Stinger size).


And I have some questions, this flashlight will be used for LE work and probably used every night I work......however, it may be used on-and-off from 20 minutes to a couple of hours a night.





1.) Whether I use the light or not, should I recharge the batteries every night so that they are fresh for the next day?



2.) What is the shelf-life of the batteries? (If there sitting for a month and then I put them in my flashlight, will they be drained?)



3.) Should I rotate the batteries, or should I use one until it dies (roughly 2-3 years) and then replace it?



4.) If the batteries have been sitting for a month and not used, should I charge them?



5.) If the batteries have been sitting for 1 to 3 weeks, should I throw them on the charger before I use them?



6.) How long should it take to charge these batteries?



7.) Is it ok to leave the batteries in the charger long term?





Thanks in advance.


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[DM51]

Your questions belong in the Batteries sub-forum, so I'm moving this there now.

 

[SilverFox]

Hello HEDP,

I would suggest that you have a spare cell available, then you can do some tests.

First of all, you need to determine how long the light will run.

Next you have to determine what an average amount of time is that you use the light each night.

Now you have to look at your lifestyle, and determine how to fit charging in so that it is both convenient and easy to remember to do.

For example:

Your light may run 2 hours with a fresh charge. You may find that this is good for around 2 weeks of use. However, your lifestyle is such that it is easier to remember to charge each week. In this case, you would set up to charge the battery each week, unless other circumstances dictate otherwise.

Li-Ion cells oxidize on the inside and wear out regardless if you use them or not. The oxidation rate is most rapid with fully charged, or fully discharged cells. Also, the oxidation rate increases with increased temperature.

Battery University has a report that looks at storing Li-Ion cells fully charged versus half charged. In a year of sitting on the shelf fully charged, the cells lost more of their capacity than similar cells stored at half charge.

Originally, Li-ion cells had a life expectancy of 3 years. The newer cells seem to be going for 5 - 7 years, so there have been improvements in the electrolyte chemicals. I would suggest figuring on a 5 year replacement, and if your cells go longer than that you can adjust your replacement schedule.

Since the aging begins as soon as the cell is manufactured, I would suggest rotating cells.

There is very little self discharge with Li-Ion cells, so you can leave them for a few months and still have basically a full charge left. However, storing at a full charge can increase the oxidation rate and reduce the cycle life from your cells.

Cycle life is related to charge, and discharge, level. I have a charger that allows me to limit the charge to a lower level (4.10 volts). This only gives you about 90% of the batteries capacity, but you get a lot more cycles. Charging to 4.2 volts gives you around 400 - 500 cycles, whereas charging to 4.1 volts gives you close to 1500 cycles. You can play with the numbers and get a feel if the extra cycles will be needed based on your normal use patterns.

Li-Ion cells that I plan on storing for over a week, I usually store at about 3.8 volts, knowing that I will have to charge them before use. If you store them in a cooler location (in a zip loc bag in the refrigerator) you can expect longer life from them.

In your case, I would simply charge them up and use them. I don't believe your charger allows for charging to lower voltages. In the future, if you happen to upgrade to a hobby charger you can then re-evaluate your charging program.

It is never a good idea to leave batteries in the charger for the long term.

The length of time it takes to charge your cells depends on how discharged they are, and the charge rate of the charger. In general, if you have a fully discharged cell, you can estimate the charging time by multiplying the capacity of the cell by 1.5, then dividing that by the charge rate.

Tom

 

[Jarl]

1. Only recharge if it's actually been used.

2. Li-ions suffer very low self discharge, so they'll hold a charge for a looooong time. Certainly at least half a year. IIRC, they loose 5% in 24 hours, then just under 5%/month from then on.

3. li-ions get worse as they age. If you only need one cell, I'd keep one at 100% charge, one in the light, and one at 40% charge in a cool place- 40% charge is best for long term storage. If your cells begin to get a bit worn, then charge up the unused cell and do a little comparo to see if you have actually lost performance. Or, more likely, charge it to full when you get another 18650 light

4. You can, I probably wouldn't.

5. You can, I definitely wouldn't.

6. Depends on the charger. Li-ion don't really charge faster than 3 hours from fully drained, though. Generally speaking, divide the capacity by the rate of charge, and add a half an hour, and you're roughly there.

7. Depends on the charger, it might be ok, it might not. However, it's never a bad thing to take a battery out the charger as soon as it's done, though if you leave it in it can overcharge and explode (v. bad)


edit: Hehe, Should have hit refresh before posting this! Great info, as usual, Silverfox =)

 

[HEDP]

1. Only recharge if it's actually been used.

2. Li-ions suffer very low self discharge, so they'll hold a charge for a looooong time. Certainly at least half a year. IIRC, they loose 5% in 24 hours, then just under 5%/month from then on.

3. li-ions get worse as they age. If you only need one cell, I'd keep one at 100% charge, one in the light, and one at 40% charge in a cool place- 40% charge is best for long term storage. If your cells begin to get a bit worn, then charge up the unused cell and do a little comparo to see if you have actually lost performance. Or, more likely, charge it to full when you get another 18650 light

4. You can, I probably wouldn't.

5. You can, I definitely wouldn't.

6. Depends on the charger. Li-ion don't really charge faster than 3 hours from fully drained, though. Generally speaking, divide the capacity by the rate of charge, and add a half an hour, and you're roughly there.

7. Depends on the charger, it might be ok, it might not. However, it's never a bad thing to take a battery out the charger as soon as it's done, though if you leave it in it can overcharge and explode (v. bad)


edit: Hehe, Should have hit refresh before posting this! Great info, as usual, Silverfox =)

Thanks guys.


With this:

Generally speaking, divide the capacity by the rate of charge, and add a half an hour, and you're roughly there.

How do you know what capacity and rate of charge is?



Your talking to a guy who failed the community college math pre-requisite 3 times and Algebra. lol

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[SilverFox]

Hello HEDP,

Let me give you a little help on this...

The cells usually have the capacity on the label. Let's work through an example.

If the cells are 2400 mAh, and I believe that charger charges at 450 ma, we can figure out the charge time by taking 2400 and multiplying it by 1.5. This gives us 3600. Now we divide that by 450 and end up with a charging time estimate of around 8 hours.

Tom

 

[HEDP]

Hello HEDP,

Let me give you a little help on this...

The cells usually have the capacity on the label. Let's work through an example.

If the cells are 2400 mAh, and I believe that charger charges at 450 ma, we can figure out the charge time by taking 2400 and multiplying it by 1.5. This gives us 3600. Now we divide that by 450 and end up with a charging time estimate of around 8 hours.

Tom

Ah, thanks. That helps a lot.


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[HDCharlie]

Hello HEDP,
Cycle life is related to charge, and discharge, level. I have a charger that allows me to limit the charge to a lower level (4.10 volts). This only gives you about 90% of the batteries capacity, but you get a lot more cycles. Charging to 4.2 volts gives you around 400 - 500 cycles, whereas charging to 4.1 volts gives you close to 1500 cycles. You can play with the numbers and get a feel if the extra cycles will be needed based on your normal use patterns.

Tom

What charger do you use that allows you to charge to less than full capacity? I would really like to have one of those!!! TIA

 

[SilverFox]

Hello HDCharlie,

I use a Schulze charger, but most of the hobby chargers offer two settings for charging Li-Ion cells. One is Li-Ion and charges to 4.1 volts and the other is Li-Po and charges to 4.2 volts. There is also a third setting for LiFe cells and it charges to 3.6 - 3.8 volts.

Tom

 

[HDCharlie]

Hello HDCharlie,

I use a Schulze charger, but most of the hobby chargers offer two settings for charging Li-Ion cells. One is Li-Ion and charges to 4.1 volts and the other is Li-Po and charges to 4.2 volts. There is also a third setting for LiFe cells and it charges to 3.6 - 3.8 volts.

Tom

Hi Tom,

Looked up the Schulze chargers. There are several. Do you recommend a particular model?

Charlie

 

[SilverFox]

Hello Charlie,

The Next 6.30-5 is a good entry level unit...

I have the isl 6-330d/RS, but I don't think they are available anymore.

Hyperion and Bantam are also very good chargers, and one of the Bantam models has an AC power supply built in. It works off of both 12 volts and AC power. I believe it is the Bantam 6.

Tom

 

[HDCharlie]

Wow, $370 is an entry level model! I think I'll have to stick with my Pila and just have to replace batteries more often. Even at 500 charges per cell, they ought to last me for several years. Thanks for your help SilverFox.

Charlie