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Old 06-02-12, 05:40 PM   #1
Burton
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Battery life expectancy

Lithium batteries have a life expectancy - either an expected shelf life or a maximum number of cycles before they are no longer functional. Things that decrease life expectancy are: deep discharging, frequency of use and storage temperature and charge state.

300 to 500 cycles are projected for most lithium batteries, with some higher end batteries rated for 1,000 cycles. My own choice for batteries was a capacity that only required charging once a week. Projecting that should give a life expectancy that should be almost identical for cycles and shelf life - about 5 years.

How do you estimate your own batteries will make out based on frequency of charge? Anything that needs recharging on a daily basis will probably need replacing after not much more than a year. Was battery replacement frequency and annual cost a consideration in your light purchase?

Last edited by Burton; 06-02-12 at 05:48 PM.
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Old 06-03-12, 08:41 AM   #2
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The ability to replace the battery was a factor that made me decide to go with my current light setup for my commuter which is 2 x Cygolite Expilion 350s. For the rear I use blinkies (a Radbot 1000 and a PB Superflash Turbo) powered by triple A recheargeable batteries. One thing I also realized after using the Cygolites is that I like their regulated feature and also the low battery indicator. The lights don't dim even while in use even when the low battery indicators start to blink.

I usually start charging the lights even before the low battery indicators start blinking to avoid the possibility of deep discharge.
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Old 06-03-12, 11:34 AM   #3
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I think 5 years is very optomistic. 1000 cycles might be possible with a lab quality cell and lab quality charger, but 300-500 seems more likely. Assuming a 3hr pack, that means you are using the light about 3hrs per week - very little compared to commuters, year round riders and dedicated night riders who might need that much every other day in the dark times of the year.


The major flaw in equating 300 cycles to 300 weeks is that LiIons loose capacity over time, so 2 years out you will need to cycle it more often thereby aging it even faster. LiIons can loose 10-20% of their capacity each year (depends on starting cell quality and which source you go by). At best, after 2 full years a 3 hr pack can only be expected to run 2.5 hours and perhaps only 2 hours with lower quality cells. By the second winter, the commuter or regular night rider is going to have to charge it more often, thus aging it faster.


By the third winter there are 2 or 3 new generation of lights out there, so a whole new light is a consideration, making replacement cost almost moot.
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Old 06-03-12, 02:56 PM   #4
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I think 5 years is very optomistic. 1000 cycles might be possible with a lab quality cell and lab quality charger, but 300-500 seems more likely. Assuming a 3hr pack, that means you are using the light about 3hrs per week - very little compared to commuters, year round riders and dedicated night riders who might need that much every other day in the dark times of the year.


The major flaw in equating 300 cycles to 300 weeks is that LiIons loose capacity over time, so 2 years out you will need to cycle it more often thereby aging it even faster. LiIons can loose 10-20% of their capacity each year (depends on starting cell quality and which source you go by). At best, after 2 full years a 3 hr pack can only be expected to run 2.5 hours and perhaps only 2 hours with lower quality cells. By the second winter, the commuter or regular night rider is going to have to charge it more often, thus aging it faster.


By the third winter there are 2 or 3 new generation of lights out there, so a whole new light is a consideration, making replacement cost almost moot.
There seem to be a lot of assumptions in your somewhat lengthy analysis and for some reason absolutely no questions. My own estimates are based on the batteries I personally bought - not what you think I bought, and the capacity I happen to be personally using - no what you think I might be using. I'm guessing from your post you plan on updating your lights regularly - I don't. The LED units have a lifetime warranty and the lipo batteries have a three year warranty. And when it comes time - I'll likely be able to just update the LEDs and keep the housings, batteries and everything else. But I doubt that'll be anytime soon - there are lots of cars on the road that put out less light.

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Old 06-03-12, 03:01 PM   #5
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The ability to replace the battery was a factor that made me decide to go with my current light setup for my commuter which is 2 x Cygolite Expilion 350s. For the rear I use blinkies (a Radbot 1000 and a PB Superflash Turbo) powered by triple A recheargeable batteries. One thing I also realized after using the Cygolites is that I like their regulated feature and also the low battery indicator. The lights don't dim even while in use even when the low battery indicators start to blink.

I usually start charging the lights even before the low battery indicators start blinking to avoid the possibility of deep discharge.
Rechargable AAA batteries are relatively inexpensive and easy to come by - good choice! Most AA and AAA chemisteries are OK to discharge completely though - in fact its better for them!

So how long are your rechargables lasting you?

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Old 06-03-12, 07:52 PM   #6
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300 to 500 cycles are projected for most lithium batteries, with some higher end batteries rated for 1,000 cycles. My own choice for batteries was a capacity that only required charging once a week. Projecting that should give a life expectancy that should be almost identical for cycles and shelf life - about 5 years.
I thought they typically degrade to 50% capacity after 3 years. Keep em half charged in the freezer I guess.
http://en.wikipedia.org/wiki/Lithium...tery#Cell_life
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Old 06-03-12, 08:34 PM   #7
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Most of my single 18650 battery suffers PCB failure well before they have degraded. My battery pack gets imbalaced before and damage before their life expectancy. That being said, I don't expect full expectancy from my cell or packs.
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Old 06-03-12, 08:35 PM   #8
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I thought they typically degrade to 50% capacity after 3 years. Keep em half charged in the freezer I guess.
http://en.wikipedia.org/wiki/Lithium...tery#Cell_life
Yup - build quality, state of charge, storage temperature and discharge rate apparently all affect the rate at which a Lithium ion battery will lose capacity. So my own strategy was to buy higher quality batteries with factory matched cells, and a capacity large enough that they can perform well with only a partial charge. That means I can expect to run them with less than a full charge for extended periods without deep discharging them, and that they'll still do the job even if they have lost capacity over a few years. Using an intelligent charger with cell balancing capabilities probably doesn't hurt either.

One thing I did learn from a lot of experience with different brands, grades, chemistries and capacities of rechargable AA and AAA cells is that 'quality' can be a relative thing. Short term performance is easy to accomplish. Predictable long term performance is almost always more expensive and never sets records for short term performance.

One option I picked when ordering batteries was the ability to 'link' batteries using a second interconnecting cable. Basicly that means I can double the capacity by clipping two packs together. Or in a few years still have the performance of one new pack by clipping two together. In the real world that means I can currently run 900 lumans for up to 18 hours continuously, or up to 5,400 lumens for up to 3 hours continuously, at my discretion. A twin battery pack fits nicely in a single water bottle cage.

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Old 06-03-12, 08:49 PM   #9
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Most of my single 18650 battery suffers PCB failure well before they have degraded. My battery pack gets imbalaced before and damage before their life expectancy. That being said, I don't expect full expectancy from my cell or packs.
Hi Colleen - are you building your own battery packs? I guess the other question is - are you using a charger with cell balancing capabilities?

Suspect we're looking at very different approaches as I deliberately chose high capacity 3 cell battery packs wired to deliver 11.1V, a lower amperage draw and with the voltage protection cut-off circuitry built into the light, not the battery. IMO that kept things simple, lighter and cell balancing is handled by the charger.
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Old 06-03-12, 09:21 PM   #10
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Hi Colleen - are you building your own battery packs? I guess the other question is - are you using a charger with cell balancing capabilities?

Suspect we're looking at very different approaches as I deliberately chose high capacity 3 cell battery packs wired to deliver 11.1V, a lower amperage draw and with the voltage protection cut-off circuitry built into the light, not the battery. IMO that kept things simple, lighter and cell balancing is handled by the charger.
I've used some Panasonic NCR unprotected 2900 using Batteryspace 2s2p cell holder. I chose the cell holder over building a pack so that I can remove the cell and periodically check and balance them. Another reason for that holder is that I personally test the built in PCB and noted it can load to the 5 amps claim. I was running an Olympia 3x XML and the Xera off the same pack. The combine drew 4 amps. At that level, I am working the panasonic hard. I noticed how much easier it is to umbalance the cell under a hard load and deep discharge. I can up it and do 6 cell if I build my own pack but I carry the 4cell in my pocket, so extra weight or bulk is not too appealing. I don't expect my cell to last longer than 2-3 years since I am pretty sure the internals are getting damage slowly. I think the IR of the cell are increasing ever so slightly with each cycles.
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Old 06-03-12, 11:22 PM   #11
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I've used some Panasonic NCR unprotected 2900 using Batteryspace 2s2p cell holder. I chose the cell holder over building a pack so that I can remove the cell and periodically check and balance them. Another reason for that holder is that I personally test the built in PCB and noted it can load to the 5 amps claim. I was running an Olympia 3x XML and the Xera off the same pack. The combine drew 4 amps. At that level, I am working the panasonic hard. I noticed how much easier it is to umbalance the cell under a hard load and deep discharge. I can up it and do 6 cell if I build my own pack but I carry the 4cell in my pocket, so extra weight or bulk is not too appealing. I don't expect my cell to last longer than 2-3 years since I am pretty sure the internals are getting damage slowly. I think the IR of the cell are increasing ever so slightly with each cycles.
Those are nice lights Colleen! But yeah - that lower voltage (7.4V) draws a higher amperage to produce those lumens and will be harder on the batteries. Have you looked at RC batteries at all? I have a couple 11.1V 6.6Ah packs that will support a 150A draw continuously. Complete overkill, but I wanted them for testing multiple lightheads. Leads on those are 12AWG silicone coated and the packs are available in different voltages and are still small enough to fit in a pocket.

Current draw was one reason I decided to go with something outside the bicycle industry myself. 10W 900 lumen P7 units with projector lenses and oversized heat sinking will draw only 0.75A each at 12V, so stacking 4 to 6 of them still doesn't even get a battery warm.
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Old 06-04-12, 07:46 AM   #12
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Those are nice lights Colleen! But yeah - that lower voltage (7.4V) draws a higher amperage to produce those lumens and will be harder on the batteries. Have you looked at RC batteries at all? I have a couple 11.1V 6.6Ah packs that will support a 150A draw continuously. Complete overkill, but I wanted them for testing multiple lightheads. Leads on those are 12AWG silicone coated and the packs are available in different voltages and are still small enough to fit in a pocket.

Current draw was one reason I decided to go with something outside the bicycle industry myself. 10W 900 lumen P7 units with projector lenses and oversized heat sinking will draw only 0.75A each at 12V, so stacking 4 to 6 of them still doesn't even get a battery warm.
I actually did consider the higher current battery. Two of my AW batteries went Looney Tune on me at the time. One kept shutting off while the other drop to 1.4v for no apparent reason. I stripped out the PCB and the bare batterries were fine. I had another set that was bought at the same time with the same amount of cycle so I decided to use those in a pack.

I also had to consider the safety of the higher current batteries. Since part of my commute involve taking a train that goes underground, I thought about the "what if" scenerio if there were a short in my wire or battery system while I was on the train. Not many places for me to dump the pack while in a underground tunnel Hence, I chosed the other chemistry battery.
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Old 06-06-12, 06:10 PM   #13
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I actually did consider the higher current battery. Two of my AW batteries went Looney Tune on me at the time. One kept shutting off while the other drop to 1.4v for no apparent reason. I stripped out the PCB and the bare batterries were fine. I had another set that was bought at the same time with the same amount of cycle so I decided to use those in a pack.

I also had to consider the safety of the higher current batteries. Since part of my commute involve taking a train that goes underground, I thought about the "what if" scenerio if there were a short in my wire or battery system while I was on the train. Not many places for me to dump the pack while in a underground tunnel Hence, I chosed the other chemistry battery.
That sounds like you - looking out for other people first!
Thought about 'batterypack meltdown' issues myself, but as far as I know there's only a risk when there's a current flow so I keep my battery packs disconnected when not actively in use. Do you think I'm being overly optomistic?
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