Lithium-ion Battery Life

[oregon]

Hello all

I just read in the manual of the Wisper 905se that the battery has a life of 300 cycles. In my calculations, that equates to around 3 years. Is that right?

Considering a replacement battery costs over £300, it seems very expensive.

Do batteries really need replacing after this time?

Thanks for your advice.

Kam

 

[Nick]

I'm sure someone with a bit more technical knowledge will be along, but a lot seems to be down to the battery/charger management system and maintenance. My understanding is that after an initial 'conditioning' period of 2-4 complete or near complete charges and dischargers, lithium ion batteries should be re-charged as often as possible, from as high a state of charge as possible; batteries should not be allowed to get too hot or too cold - I keep mine indoors during the winter, for example. It's not quite 'set and forget' but, doing this, I and a couple of other BionX users I know of are getting the same speed and range from our bikes two years down the line. I think the BionX batteries cost something hideous like £500 so we'll see how the next year goes....

 

[flecc]

Some claim lithium ion batteries can accept 500 full charges but experience to date suggests that's too optimistic, for most of them a maximum of 400 charges is more like it and 300 wouldn't be unusual.

For someone commuting a full charge distance five days a week, that could be as little as a year and a quarter to a year and a half, though most people would probably get two years use from he latest ones. A select few expensive ones last longer, like the BionX one that Nick mentions, and we hope the Panasonic ones also.

So electric bikes aren't the very cheap option they might appear at first, given the replacement battery costs of £300 to £600 for some bikes.

However, consider the cost of the alternatives. Both driving a car with today's petrol prices and public transport would be hugely more expensive, though a moped would compete, often being as cheap or cheaper to buy and run than an e-bike. Not so if as a result of the lack of exercise you take up a gym membership though.
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[kraeuterbutter]

lithium ion batteries should be re-charged as often as possible, from as high a state of charge as possible;

hmm.. i would not realy agree with that from what i have learned so far

yes, you should not run them down too much all time..
but keeping them on a very high charge-level all time is also not good..

Welcome to Battery University

so: when you for example drive only once a week with the bike, i would think it is better to charge it the day befor you drive instead of charging it after you have driven it
so it does not stay too long at over 4Volt/cells..

i would charge it after driving (if i have emptied the battery) immediatley up to 3,8Volt/cell (so: if a full charge lasts 4 hourse i would charge it for 1-2hours and then let it rest)

the rest i would charge before i use the bike (or the day before)

 

[flecc]

In some cases the better bike makes have their lithium battery chargers set to only go to the optimum level rather than the fullest possible charge. That's why Panasonic for example make it possible to give a two year guarantee on their latest lithium batteries, the sophisticated charging and usage control keeping the battery within the best parameters.

That Battery University chart was mainly intended to show the effects of long term storage at different temperatures. At British ambient temperatures, well below 20 degrees C on average over the year, the very short term loss at full charge is quite small and it's probably not worth the daily inconvenience of two level charging. Charging and keeping in the coolest location could be worth it though.

For a daily user like a commuter, two stage charging would not be practical, unless their two way trip was done on one charge. Then they could charge at work, the battery ready in time for the ride home where it would be at part charge overnight. That would also save the cost of the electricity at home too.
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[kraeuterbutter]

yes, for a daily commuter it may be different

for somebody who rides his bikes on weekend, maybe 2,3 or 4 charges
and then let the bike rest during the week it maybe be different

longtime-storage: for me using the bike/battery every or every second weekend is not much difference to long-time-storing..


storing the battery 6 months --> 6 * 30 * 24 = 4300 hours of storing

using the battery in this 6months every weekend (charge befor use and then use it)
its maybe 26 weekends, 2 hours for charging each week, 2 hourse of using
makes: 104 hours of charging/using

so the difference between long-time-storing (6month = 4300 hours)
or "use-it-every weekend" (= 4200hours of storing)
seems not to be that different to me


for a daily commuter:
when i charge the battery in the evening, driving in the morning to my work-place, the bike is also not at very high charge-level for long..
maybe 2-3 hourse before i start driving, and after the first few km the charge-state goes down so for the rest day until recharging iam not that high with charge-state

(so: this was fast written, and i fear not 100% understandable what i mean because of my bad English ;( sorry for that)

 

[RobNYC]

Sooo... would it make sense for me to charge in the early morning if I am going to use the battery mid or late morning to go to work? Charging at work isn't an option for me.

If I can get significant more battery life, I would put the charger on a timer to start at 4 or 5am instead of charging it at 6 or 7pm when retuning from work.

 

[kraeuterbutter]

if you build your batterys by yourself:

invest a little more money and go the Fepo4-line..
1000cycles should be realy no problem (i bet you get lot more in an e-bike with them)

after 3 years when you need a new LiIon the A123 have paid there initial higher costs

 

[flecc]

Sooo... would it make sense for me to charge in the early morning if I am going to use the battery mid or late morning to go to work? Charging at work isn't an option for me.

If I can get significant more battery life, I would put the charger on a timer to start at 4 or 5am instead of charging it at 6 or 7pm when retuning from work.

The life gain in that circumstance would be miniscule with daily use Rob, but you would have a very slight gain in initial performance with the battery fresh off the charger, though that would only last the first mile or so. So it could yield a very small two way gain.
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[flecc]

(so: this was fast written, and i fear not 100% understandable what i mean because of my bad English ;( sorry for that)

Completely understandable kraeuterbutter, no apology needed.
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[Jeremy]

Whilst I agree that one or two lithium chemistry cells have a short cycle life, this is very far from being a very broad generalisation that applies to all lithium chemistries.

Very early lithium ion chemistry cells had cycle lives that were of the order of a few hundred cycles at best. Newer chemistries are very much better though, 3000 cycles or more is readily attainable from LiFePO4 if charge/discharge depth is limited to less than about 70 or 80%, which it would be for most ebike users, I believe. Even with full charge and discharge LiFePO4 cells will do around 1000 cycles.

Other lithium chemistry cells are also pretty good with regard to cycle life. The Sony Konion LiMn cells seem to hold up well for around 1000 cycles, provided discharge rates are kept to no more than about 3C. I have a feeling that cycle life has as much to do with manufacturing techniques and application design as it does with cell chemistry. I strongly believe that ebike battery failure causes are dominated by poor design, with cells being poorly managed, both on discharge and charge. A good BMS would most probably very significantly extend the life of any lithium battery pack.

Jeremy

 

[flecc]

I'm sure that's true Jeremy, my post above referring to current bikes of course, none with lithium iron and hardly any with the best BMS, judging by the battery performances that we've been seeing.

In this respect on current bikes and kits, I'd only be trusting of the Panasonic and BionX systems in the present state of the market.
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[RobNYC]

The life gain in that circumstance would be miniscule with daily use Rob, but you would have a very slight gain in initial performance with the battery fresh off the charger, though that would only last the first mile or so. So it could yield a very small two way gain.
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Thanks Flecc... probably not worth the trouble.

 

[fishingpaul]

If you just did a two or three mile trip, and were only planning another three mile trip the following day, would you charge a lithium battery after each trip.

 

[the_killjoy]

Of course in two years battery technology will have moved on so by then you will probably get more for your money anyway.

 

[JohnInStockie]

Of course in two years battery technology will have moved on so by then you will probably get more for your money anyway.

Battery tech seems slower than most tech these days, prob cos no-one is looking for a solution with fuel cells being the great hope.

 

[the_killjoy]

And people say that I see it the glass half empty, I am just trying to justify the cost of the bike!

 

[flecc]

If you just did a two or three mile trip, and were only planning another three mile trip the following day, would you charge a lithium battery after each trip.

On the longer range ones I wouldn't bother Paul. For example, on the 14 Ah Wisper battery I'd do the whole week at 3 miles a day before charging. With a bike having only 10 to 15 miles range I probably would charge each time to maintain full performance, since that drops off as the battery empties.
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[kraeuterbutter]

Battery tech seems slower than most tech these days, prob cos no-one is looking for a solution with fuel cells being the great hope.

hmm.. iam in the rc-hobby for meanwhile 20 years...
and when it comes to batteries the improvments were HUGH...

i remember the first electric plane, with 6cells and 1200mah Nicd
meanwhile at the same size and weight we have Nimh doing 3000mah
and Lipos with 8000mah

the 1200mah Nicd could do 15A
the same heavy Lipos now can do 150A

compare e-bikes 10 years ago and now..
12V and 10Ah heavy acid batteries with short cycle-life

now: 36V and 10Ah with lot less weight, longer lifetime and more power..

 

[Jeremy]

You're absolutely right about improvements in batteries. These aren't just in the past year or two either. I'm scribbling this on a laptop that was made in 2003. It gets used on battery power alone for at least 2 hours each day and shows no real signs of battery failure. It will still do around 3 hours on a full charge, pretty much as it did when new nearly 5 years ago (I think it would do about 3 1/2 hrs maximum when new, so it may have lost about 15% of it's original battery capacity).

The battery looks to have Sony LiMn cells in it, as far as I've been able to tell.

Given that even 5 year old lithium cells can have a long life and give well over 1000 charge/discharge cycles I can't see why ebikes couldn't be at least as good. As I mentioned before, I'm certain that the right cells, with the right BMS, could work as well as the ones in my laptop do. Quite why ebike manufacturers can't get something like this right I don't know - it's not rocket science to design and build an effective BMS, nor is it expensive.

Jeremy