When should Li-Ion Battery be Charged?- Mtbr.com
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  1. #1
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    When should Li-Ion Battery be Charged?

    Just wondering if it is better to charge after a ride or leave the battery 1/2 charged until the day of the next ride? Does it matter?

  2. #2
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    For storage, leave it around half charged if you are fussed about prolonging capacity.

    Read this: http://www.batteryuniversity.com/parttwo-34.htm

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    Quote Originally Posted by womble
    For storage, leave it around half charged if you are fussed about prolonging capacity.

    Read this: http://www.batteryuniversity.com/parttwo-34.htm
    Yep...unless you are dead sure you are going out the next night I'd not charge the batteries till just before the next night ride.

    On a side note: I've known about the BU link for years but Damn!...I didn't know about that stuff concerning the "Digital fuel gauge memory effect". I've not heard that before. Don't want to get too far off topic but has anyone had any problems with their fuel-gauge being off-tilt? ( as suggested by the link )

  4. #4
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    Yes, it happens with my DSLR battery - the charger has a calibrate function that essentially drains it and full charges it. It also happens with my laptop battery. The fuel gauge cannot get the actual drain on the capacity of the battery perfect so over time it gets out of whack. You reset that by draining it and full charging it.

    If you have a choice between leaving the battery empty or charged, pick charged. Long term storage the 40% thing is good. However, your Li-ion battery is going to die probably more from old age (3 years or so) rather than from charging it too much. That said, you might as well charge it so it's ready to go when you need it.

    J.

  5. #5
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    Quote Originally Posted by JohnJ80

    If you have a choice between leaving the battery empty or charged, pick charged. Long term storage the 40% thing is good. However, your Li-ion battery is going to die probably more from old age (3 years or so) rather than from charging it too much. That said, you might as well charge it so it's ready to go when you need it.

    J.
    They will last a lot longer than 3 years if you don't leave them fully charged for long periods of time. The life of a li-ion pack is primarily determined by the number of charge cycles and the total amount of time they sit at high levels of charge which causes rapid deterioration of the cells. It's really bad of they sit at a high percentage of charge and high temps for long periods of time. That's why laptop packs have such a short life. They sit at near full charge and it's hot inside a laptop when it's running while plugged in.

    I have some li-ion bike light packs that are going on 6 years now and are still going strong. I try to keep them between 30%-70% of charge most of the time. I only charge them up to 100% if I actually need the full runtime and I do that right before using the pack. If you really want to extend the life, you need a charger where you can set the upper charge voltage limit so you can essentially set the ending % of charge. But you can get most of the benefits by waiting to charge them before riding and by not storing them for the off season at a high percentage of charge. 40-50% is ideal for storage.

  6. #6
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    Their capacity begins to diminish pretty strongly after about 3 years give or take. That's been true of my camera batteries, my laptop batteries and that is what the engineers at one of the major producers of them told me when I used to sell them/work for them (OEM) and visited their factories routinely. The problem is that the chemistry sort of loses it's ability to hold charge over time whether you use them or not (I'm not a chemist - I'm an electrical engineer).

    Whatever you are doing to your cells, it isn't found too often and you are a lucky guy - I also wouldn't bank on that performance as normal because it's not what the manufacturers see in their life testing.

    J.

  7. #7
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    Quote Originally Posted by MtbMacgyver
    They will last a lot longer than 3 years if you don't leave them fully charged for long periods of time. The life of a li-ion pack is primarily determined by the number of charge cycles and the total amount of time they sit at high levels of charge which causes rapid deterioration of the cells. It's really bad of they sit at a high percentage of charge and high temps for long periods of time. That's why laptop packs have such a short life. They sit at near full charge and it's hot inside a laptop when it's running while plugged in.

    I have some li-ion bike light packs that are going on 6 years now and are still going strong. I try to keep them between 30%-70% of charge most of the time. I only charge them up to 100% if I actually need the full runtime and I do that right before using the pack. If you really want to extend the life, you need a charger where you can set the upper charge voltage limit so you can essentially set the ending % of charge. But you can get most of the benefits by waiting to charge them before riding and by not storing them for the off season at a high percentage of charge. 40-50% is ideal for storage.
    http://www.batteryuniversity.com/parttwo-34.htm

    Aging of lithium-ion is an issue that is often ignored. A lithium-ion battery in use typically lasts between 2-3 years. The capacity loss manifests itself in increased internal resistance caused by oxidation. Eventually, the cell resistance reaches a point where the pack can no longer deliver the stored energy although the battery may still have ample charge. For this reason, an aged battery can be kept longer in applications that draw low current as opposed to a function that demands heavy loads. Increasing internal resistance with cycle life and age is typical for cobalt-based lithium-ion, a system that is used for cell phones, cameras and laptops because of high energy density. The lower energy dense manganese-based lithium-ion, also known as spinel, maintains the internal resistance through its life but loses capacity due to chemical decompositions. Spinel is primarily used for power tools.

    The speed by which lithium-ion ages is governed by temperature and state-of-charge. Figure 1 illustrates the capacity loss as a function of these two parameters.

    The worst condition is keeping a fully charged battery at elevated temperatures, which is the case with running laptop batteries. If used on main power, the battery inside a laptop will only last for 12-18 months. I must hasten to explain that the pack does not die suddenly but begins with reduced run-times.

    The voltage level to which the cells are charged also plays an important role to longevity. For safety reasons, most lithium-ion cannot exceed 4.20 volts per cell. While a higher voltage boosts capacity, the disadvantage is lower cycle life. Figure 2 shows the cycle life as a function of charge voltage.

  8. #8
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    Quote Originally Posted by Maximus_XXIV
    http://www.batteryuniversity.com/parttwo-34.htm

    Aging of lithium-ion is an issue that is often ignored. A lithium-ion battery in use typically lasts between 2-3 years. The capacity loss manifests itself in increased internal resistance caused by oxidation. Eventually, the cell resistance reaches a point where the pack can no longer deliver the stored energy although the battery may still have ample charge. For this reason, an aged battery can be kept longer in applications that draw low current as opposed to a function that demands heavy loads. Increasing internal resistance with cycle life and age is typical for cobalt-based lithium-ion, a system that is used for cell phones, cameras and laptops because of high energy density. The lower energy dense manganese-based lithium-ion, also known as spinel, maintains the internal resistance through its life but loses capacity due to chemical decompositions. Spinel is primarily used for power tools.

    The speed by which lithium-ion ages is governed by temperature and state-of-charge. Figure 1 illustrates the capacity loss as a function of these two parameters.

    The worst condition is keeping a fully charged battery at elevated temperatures, which is the case with running laptop batteries. If used on main power, the battery inside a laptop will only last for 12-18 months. I must hasten to explain that the pack does not die suddenly but begins with reduced run-times.

    The voltage level to which the cells are charged also plays an important role to longevity. For safety reasons, most lithium-ion cannot exceed 4.20 volts per cell. While a higher voltage boosts capacity, the disadvantage is lower cycle life. Figure 2 shows the cycle life as a function of charge voltage.
    Yep, that about sums it up. In conclusion, If you use 18650 cells every day and need to charge them daily then expect about two years of reliable use. If you use cells only occasionally and only charge them when needed ( not storing them in a hot environment ) I think you can expect they will last a bit longer ( provided you don't abuse them by storing them in a hot environment with a full charge ). I have cells that see only intermittent use. They are about 2.5 yrs old and still seem to work fine. As long as I get reliable use from them I will continue to use them. Since they were only $5 a cell I think it's safe to say that I got my money's worth from them.

    On the other hand I have a couple LIR123A ( or 16340 )Li-ion cells that have bellied-up and no longer hold a charge. Strangely, some of my older ones ( light purple ) (3 yrs old) are still working while the newer ( ~ 2yrs old ) blue cells are bellied-up. Maybe the blue no longer work because I stored them with a full charge, who knows. Oh, what-the-hey...they were only $2.50 a cell so who cares. I now own a couple black/red/fire Trustfire 16340's cells. ( 880mAh ) These will see daily use in my pocket mini-cree Q5 5-mode. If I get two years out of them I will be thrilled. At ~ $2.50 per cell these are SO much better than buying cheap disposable AAA cells.

  9. #9
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    Most of the information on battery university is very good. The "typically lasts between 2-3 years" statement is just that a typical lifetime. It's also slightly dated information as high quality 18650 cells have improved in the last few years. Bike light packs are actually a pretty favorable application for li-ion cells. They normally aren't exposed to high temperature, the discharge rates are relatively low in most applications (especially lights that use buck converters), and the cycle life typically isn't extreme. So if you follow good charge and storage practices you can easily get lifetimes longer than 2-3 years.

    Another application of Li-ion 18650 cells that goes out of their way to achieve good battery pack life by following very good practices is Tesla Motors. They rate the pack life in the Tesla Roadsters at 5 years. Here's some details about the practices they employ.

    http://www.teslamotors.com/blog2/?p=39

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