Battery end of life: What happens?

[aroncox]

Sorry if this has been asked before (and I suspect it must have been), but my serching turned up nothing, probably becuase i couldn;t think of what terms to search for. So pelase feel free to point me to any earlier posts there may be.

My question is: What happens when the battery is getting near to time for a replacement?

I have a Li-Ion battery and and I'm having problems with my bike that could be battery related, and I want to make sure it's not just that I need a new battery. So, does it just limit the distance more and more until it stops working, or does it limit the power too, or something else.

I've had mine for over a year, and it gets charged twice a day (on week days) but I hoep I don;t need a replacement as £250 a year for a new battry is not cheap!

 

[flecc]

With all battery types the range gradually shortens until it's no longer sufficient.

In parallel with that, the performance also tends to drop off, since with age the internal resistance of the cells increases, making it more difficult for the charge to flow out freely.

Lithium batteries used with high power motors have the additional factor of cut-out under high load due to voltage drop, the incidence of this increasing as cell resistance rises with age. That can determine end of life when a bike has to be used under high load conditions such as in a very hilly area. That same battery could then be used by someone in a flat area for another year or so maybe, especially if the second rider was a strong cyclist making only light assistance demands.

All these factors make the prediction of lithium battery life nearly impossible without detailed knowledge of each owner, their usage, and the usage circumstances.

However, one year failure is unlikely with normal use. If a Li-ion battery is ridden in a very hot climate to nearly empty every day and therefore fully recharged then each day, the capacity could drop as much as 60% in a year, and with it, 60% of the range lost. For us in the UK though, that's extremely unlikely, and early adopters are reporting about 35% loss in one year.
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[nigel]

Nigel

Also just out of intrest what does everyone do with there batterys when the life is gone with lithuim is that it i know with SLA they can be recharged. thanks NIGEL

 

[flecc]

The contents can be recycled Nigel, but the local authorities don't have facilities for that yet. However, it's best to dispose of them at the battery recycling points in council depots as that will increasingly alert them to the need for a facility. If they don't see them, they'll never know.

In theory they could be rebuilt with new cells, re-using the electronics, but they'd need shipping back to the far eastern manufacturers as there are so many types, so that wouldn't be worthwhile at present.
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[Brangdon]

However, one year failure is unlikely with normal use.

They have a limited number of recharges; the range is given in your article here as 300-500. If this battery is being recharged twice a day, 5 days a week, it will have reached the upper end of that limit after 50 weeks, or about a year. So as it is over a year old it could well be nearing the end of its life.

Speaking as one with no experience, I think recharging twice a day is very frequent. I gather a partial recharge is as damaging as a full recharge. Your article also says that for long-term storage batteries are happiest at 40% of full charge. I conclude that recharging too often is a mistake (albeit not as bad as recharging too rarely).

My own daily commute uses about a quarter charge, and I plan to recharge at most every other day, at 50%, rather than every day, at 75%. There's an argument for every third day, at 25%, because that should be high enough to prevent damage from over-discharging, while reducing the number of recharges and letting the battery spend the most time around 40%.

It all seems a bit of a lottery, though. And if my two-way commute was much over 80% I'd probably recharge in the middle too.

 

[flecc]

Not quite like that Brangdon. The recharges should be as often as possible regardless of how little each use, and as I've said before, these small recharges are not full charges off the total number.

There is no absolute number of charges. Li-ions used in satellites are seven times the size they need to be, and during each dark cycle when out sight of the sun they use that one seventh of the capacity. Then back in the light they recharge that bit, so it's a part charge cycle every 24 hours. They last a minimum of ten years in those satellites, often very much longer, so a minimum of 3650 charges. They are perfectly normal Li-ions, chemically identical to many in use on bikes, albeit produced more carefully to eliminate possible manufacturing faults. They last like that purely because of the consistent partial use and charging and avoidance of sudden high discharges.

The storage at 40% of charge only applies to batteries out of use in very cold storage, as close to zero degrees centigrade as possible. It's important not to take bits out of context as that can be misleading, as it has been for you in this case. Batteries in use at normal temperatures last best when at full charge, very different from what you've been doing. The composite of all industry advice is to recharge as often as possible, and the longest experience of all, that in satellites, bears that out.
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[Django]

There is no absolute number of charges. Li-ions used in satellites are seven times the size they need to be, and during each dark cycle when out sight of the sun they use that one seventh of the capacity. Then back in the light they recharge that bit, so it's a part charge cycle every 24 hours. They last a minimum of ten years in those satellites, often very much longer, so a minimum of 3650 charges. They are perfectly normal Li-ions, chemically identical to many in use on bikes, albeit produced more carefully to eliminate possible manufacturing faults. They last like that purely because of the consistent partial use and charging and avoidance of sudden high discharges.

Brilliant Flecc. Just brilliant.

Thanks,

Django

 

[flecc]

Thanks Django.

Of necessity, the article Brangdon referred to was brief, but heres a fuller picture including all the information necessary on Li-ion life.

Though there's about a decade of experience with small Li-ion cells, there's very little knowledge of the consumer large capacity multi-cell batteries that we use. The first of them are reaching a year old now, and as previously predicted from laboratory testing, most reaching that are showing around 33% capacity loss, just over 35% in one case I know of. In theory in the worst conditions, the loss could reach 66% in a year.

The worst conditions are using the entire charge every time to empty, and both using and storing the battery between uses in high temperature conditions. The best conditions therefore are using the battery for a short distance each use and immediately recharging, together with operating in cool conditions with cool battery storage between uses. These part charges do not count as full charges, summing them into full charges is valid to some extent.

Additionally, lithium cells start losing life from the moment of manufacture due to chemical decay, whether used or not. If a battery is to be stored for a long period, this decay can be alleviated in the following way. The battery's state of charge should be reduced to between 20 and 40% of full charge, then placed in refrigeration as close to zero degrees centigrade as possible, but not freezing. That reduces the loss of capacity to only about 2% per year, and I do this with the Li-ion battery on my laptop as I only infrequently use it away from home on battery power. It's about four years old now and still has it's full capacity, judging by how long it runs.

The percentage capacity loss in each year is of the capacity at the start of each year, not the original capacity, so the actual loss reduces over time. Here's a chart showing what 33% annual loss means for a 10 Ah Li-ion battery with range losses as well. Pick the column starting closest to your range when new:

Year - - - Capacity - - - Range 1 - - - Range 2 - - - Range 3

1 - - - - - 10.0 Ah - - - - 30 miles - - - 20 miles - - - - 15 miles
2 - - - - - -6.7 Ah. - - - - 20.1 - - - - - 13.4 . - - - - - 10
3 - - - - - -4.5 Ah. - - - - 13.5 - - - - - -9.0. - - - - - - 6.7
4 - - - - - -3.0 Ah - - - - - 9.0 - - - - - -6.0 - - - - - - -4.5
5 - - - - - -2.0 Ah - - - - - 6.0 - - - - - -4.0 - - - - - - -3

The range can restrict someone's effective battery life, a commuter doing 15 miles each way/charge could barely reach year 3 if starting with a 30 mile range and couldn't complete year 2 if starting with a shorter range, these already born out in practice in some cases.

An overriding factor is the number of charges the battery can take. The concensus is about 500 full charges, some claiming 800, so obviously that could limit the length of life. If the bike is used daily for 300 days of the year to a quite high battery discharge, the life could again be limited to less than two years before the battery was unfit for further use due to the number of full charge cycles.

Another limiting factor is the terrain. In very hilly country with a rider not making sufficient contribution, overload cut-outs can be experienced on bikes using powerful motors, and this gets worse as capacity reduces, therefore limiting the life to the point where the cut-out frequency becomes intolerable.

All that looks a bit gloomy, but conversely, someone using a bike two or three times a week for short distance shopping or social trips in moderate terrain and charging after each use could use a battery for several years and be very happy indeed with it's life.

Only time will enable us to fully know what to expect with these batteries, and during that period further advances may make that knowledge unnecessary anyway. Meanwhile our best protection is the availability of the highest possible Li-ion capacity at the outset and I'm hoping to see some progress there for our existing bikes.

My own attitude is not to fret too much about making things perfect for the battery, just use, enjoy, and when the time comes, buy a new one.
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