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  1. #1
    vol
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    Best way to use the $20 headlight for battery life - full => 0 or partial charge?

    This is another question regarding "the popular $20 headlight" (someone added a post right after my question in that thread without addressing my question so I'm starting a new thread):

    To prolong the battery lifespan, what's the best to use this light, if I have two battery packs 1 & 2 for the light?

    a) charge 1 fully, use it half way, set it aside and use battery pack 2 from full charge until half way, then set 2 aside, use 1 (after fully charging it).... In other words, always use them from full charge to about half way, never use it all the way to totally discharged.

    b) charge 1 fully and use it all the way to totally losing the charge, then use 2 (fully charged) until half full--meanwhile, charge 1 to about half full and keep it waiting---because I read that lithium battery should be kept partially charge when not in use. Then charge 1 fully before using it. In other words, always use each battery pack from full to no charge.

    (Real experience should make more sense than theory )

    (btw for that damn tight connector, I have to use pliers to disconnect it after each ride )

  2. #2
    coprolite fietsbob's Avatar
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    better to keep a tank topped up rather than sucking sediment thru the fuel pump,

    may apply to batteries ,, I tried to recharge before they dimmed.. to dull red
    Last edited by fietsbob; 02-01-14 at 06:16 PM.

  3. #3
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    A battery has a working range or specific voltage that it shouldn't go over or under, this varies from battery types.

    read this
    http://batteryuniversity.com/learn/a...m_medium=email

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    My understanding is that lithium batteries do better when they are not run all the way down. NiMH and NiCad batteries need to be cycled (taken down to 1 volt and charged) once in a while.

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    Randomhead
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    Lithium batteries last much longer when they aren't discharged much before being recharged. Unless they are stored, when they should be at the recommended storage voltage. Which is significantly below max voltage.

  6. #6
    vol
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    Thank you all. Glad I've asked. Guess I should alternate among all my lights/batteries instead of using one until it dies.

  7. #7
    Senior Member CustomSteel's Avatar
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    Quote Originally Posted by davidad View Post
    My understanding is that lithium batteries do better when they are not run all the way down. NiMH and NiCad batteries need to be cycled (taken down to 1 volt and charged) once in a while.
    Yes, the lithium batteries go through a nasty, albeit natural, internal plating process during their lifespan. Running them down low enhances this process, which is what you don't want. This is why it's good to run your laptop off of the power cord and leave the battery out when you are able too.

    Also, as HK 45 pointed out, overcharging any of your batteries is bad for them as well.

  8. #8
    Senior Member 01 CAt Man Do's Avatar
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    Quote Originally Posted by vol View Post
    This is another question regarding "the popular $20 headlight" (someone added a post right after my question in that thread without addressing my question so I'm starting a new thread):

    To prolong the battery lifespan, what's the best to use this light, if I have two battery packs 1 & 2 for the light?

    a) charge 1 fully, use it half way, set it aside and use battery pack 2 from full charge until half way, then set 2 aside, use 1 (after fully charging it).... In other words, always use them from full charge to about half way, never use it all the way to totally discharged.

    b) charge 1 fully and use it all the way to totally losing the charge, then use 2 (fully charged) until half full--meanwhile, charge 1 to about half full and keep it waiting---because I read that lithium battery should be kept partially charge when not in use. Then charge 1 fully before using it. In other words, always use each battery pack from full to no charge.

    (Real experience should make more sense than theory )

    (btw for that damn tight connector, I have to use pliers to disconnect it after each ride )
    Personally I think you're over-emphasizing the importance of battery management, but since you did ask I can give you the best scenario for prolonging Li-ion battery life...first:

    1) you need a charger that will allow you to set the maximum charge voltage ( a hobby charger will do this ). This will allow you to charge the battery to than less than it's normal peak voltage. For a normal 2S2P 4-cell set-up this is 8.4volts. What you want to do is charge the pack to 8 volts. This helps prevent premature aging of the cells. The down side to doing this is that it will shorten the run time of the battery by 20%.

    2) ...then run the battery till it nears it's pre-set cutoff. Usually this is around 6 volts. The deeper you discharge a Li-ion battery the faster it will age. Best not to store a Li-ion battery fully charged as this also ages the battery faster. Store with less than a full charge. In a nutshell those are the technically facts.

    Realistically doing all of what I just said would be a total PITA. If you bought cheap batteries charge them to normal peak voltage ( just before you ride ) and get whatever you can get out of them. Controlling all the aging factors of a battery is very hard to do. My best advise is: Buy the best quality batteries you can. Keep the battery away from extreme heat when storing. Buy a battery with a capacity that best suits your need. If you are into long epic type of riding a larger capacity battery is what you want.

    All said, since you have two batteries I would suggest charging the batteries you want to use
    ( to full peak voltage ) just before going out. Then if you think you might ride long enough to need just a bit more run time, bring along the other battery and switch the first out when the indicator reaches red ( or if no indicator ) run the first battery till you think it is near shut-off voltage and then switch out batteries. At that point you run the second battery as long as it takes to get you out out of the woods. Keep the first battery as your reserve. If you have no voltage indicator on your lamp you will have to do a test discharge using your lamp at home so you know how much run time your battery/lamp will provide you during normal use. Just be sure to use a fan to cool the lamp if you do this.

  9. #9
    vol
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    Thank you very much for answering my specific question, 01 CAt Man Do. I get your points. Only thing is it's not practical to recharge just before the ride, since the charging takes a long time and I may ride in the morning. Maybe charge it to like 80% full in advance, then charge a little more just before leaving home. To avoid overcharging, maybe unplug the charger before the indicator turns green (so for example when it's orange color, or just after enough hours even if it's still red). The time spent for charging is one reason why I had always used alkaline battery-powered lights until after buying this light recently.

  10. #10
    Senior Member 01 CAt Man Do's Avatar
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    Quote Originally Posted by vol View Post
    Thank you very much for answering my specific question, 01 CAt Man Do. I get your points. Only thing is it's not practical to recharge just before the ride, since the charging takes a long time and I may ride in the morning. Maybe charge it to like 80% full in advance, then charge a little more just before leaving home. To avoid overcharging, maybe unplug the charger before the indicator turns green (so for example when it's orange color, or just after enough hours even if it's still red). The time spent for charging is one reason why I had always used alkaline battery-powered lights until after buying this light recently.
    Yes, that strategy would work fine. Topping off a battery that is near fully charged should work well and not take more than a couple hours. If your batteries maintain decent capacity for two to three years you've done well. I have a couple 5200mAh batteries that I've owned for at least four years. I won't use these for longer rides but they still seem to work fine. If you buy a better hobby charger some are equipped with a setting that will let you safely discharge the battery so you can measure it's true Ah rating. That would be a nice thing to have but even if you know the true Ah rating of a battery you still need to know how that will translate over to the lamp you are using. This is why it is so important to test the battery with your lamp so you don't find yourself out in the woods with a dead battery.

    Personally I never worry too much about running out of power. I always carry a small XM-L torch on my bars for back-up reserve. On it's medium setting it will provide me with about 200 lumen worth of light for *about three hours ( * with a single Panasonic 3100mAh 18650 cell ). That's more than enough light/time to get you home without too much fuss. Been doing this for years and so far I've never had to use it. That said every once in a while I turn it on just to make sure all is good.

    The only time I've ever almost been caught without enough lights/batteries was back in the days of halogen lighting. I was doing a remote ( unexplored ) mountain ride. This was back before the days of GPS as well. I was going purely by maps and bike computer for distance. Sun started going down I had at least an hour or so before I was to begin my descent. I had my old NR 10watt halogen spot helmet lamp with me with a NimH battery that had an unknown amount of charge on it. When I started down the mountain I had to bring out the NR. Luckily it got me down the mountain and back to camp. Scary as crap being somewhere you've never been before and find yourself with the sun going down. Most of that is all changed now. The newer LED lamps with Li-ion batteries will run for a real long time and if you have GPS you almost always know where you are and where you should be. Yep, back in those days I had a good scare more than a number of times. Nowadays even if I don't take my dedicated bike lamps I always carry at least one LED torch with an extra battery. Nope, this CAt will not be caught back in the woods again without a light source.

  11. #11
    Senior Member DannoXYZ's Avatar
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    I don't worry too much about abusing 18650 batteries. I get all of mine for free from Best Buy or similar computer stores. I ask for returned/rejected laptop batteries and take them apart for the 18650 cells inside. Usually just 1 or 2 is bad and the rest are perfectly fine. I charge them up and use them until cut-off. Then toss them in the charger and put the ones in the charger in the lights. They usually last 2-3 years and that's great for free batteries. I've still got 4 more Dell 14.4v batteries I need to disassemble. That'll get me another 32 18650 batteries, 25-28 of which will be good. So I'm set for another 3-5 years as far as batteries go.

    I've built a joule-thief to re-use the 'spent' AA-batteries my wife tosses away. I put them in 2s3p configuration for about 3v output. The joule-thief boosts lower output up to 3.2v through a timer/chopper circuit and inductor. This is enough to drive the XML-T6 at 2000ma for 700lm output for about 5hrs; not bad for spent AA alkaline batteries. At 3.35v & 3amp, the XML-T6 it will generate 900lm, but is lower efficiency and too much current to ask from spent AA batteries. When the booster stops working, the AA-batteries will have been drained to 0.10-15.v.

  12. #12
    aka Tom Reingold noglider's Avatar
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    Very clever way to acquire 18650 cells. I'll try that myself!

    I never heard of a joule thief, so I just read the wikipedia article on them. Thanks for the education. How much work (time) did it take to make the circuit and battery holder for your light?
    You don't read my signature anyway, do you?

    Tom Reingold, noglider@pobox.com
    Residences: West Village, New York City and High Falls, NY
    Blogs: The Experienced Cyclist; noglider's ride blog

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