Li-ion Battery Life

[flecc]

Though there's about a decade of experience with small Li-ion cells, there's very little knowledge of the 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, many 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.

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 charges, some claiming 800, so obviously that could limit the length of life. Regardless of the range they achieve, if the bike is used daily for 300 days of the year, the life could again be limited to less than two years before the battery was unfit for further use due to the number of 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.

Additionally, lithium cells start losing life from the moment of manufacture, whether used or not.

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.
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[ITSPETEINIT]

Lithium Life

POSTED BY FLECC 8/7/2007:
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

What sort of a life is that?

I posted (I think) my concerns for my Lithiums' ranges between charges: one 12 months old - declined from 28 miles to 18 miles, and 2 others - 2 months old - declined from 22 miles to 18 miles.There may be some life and some range after one year but it is becoming marginally useful.

It must be one of those laws of economics:
A Lithium battery declines in greater proportion than the use to which it is put and needed. (The greater the use the swifter, disproportionately, its decline).
Peter
PS I am hoping to run a test, using my bike, with another Lithium which will do 28 miles between charges after 12 months/1400 miles for another bike/another rider.

 

[flecc]

What sort of a life is that?

As said Peter, very satisfactory for that user. Not everybody wants to do long runs every day, and in fact the majority of e-bikes sold are used in that light use fashion. I think it's important to remember that we in a forum like this are very much the minority. The majority of buyers would never bother to look up such a forum, just buying their bikes for shopping trips and other local transport. They outnumber us dozens to one.

PS I am hoping to run a test, using my bike, with another Lithium which will do 28 miles between charges after 12 months/1400 miles for another bike/another rider.

We'd need to know what both bikes are of course Peter. Low powered models give Li-ions a comparatively easy life, and also both batteries nominal capacity, if not the same make and type.
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[ITSPETEINIT]

Now the test I promised

As said Peter, very satisfactory for that user. Not everybody wants to do long runs every day, and in fact the majority of e-bikes sold are used in that light use fashion. I think it's important to remember that we in a forum like this are very much the minority. The majority of buyers would never bother to look up such a forum, just buying their bikes for shopping trips and other local transport. They outnumber us dozens to one.



We'd need to know what both bikes are of course Peter. Low powered models give Li-ions a comparatively easy life, and also both batteries nominal capacity, if not the same make and type.
.

A Test made on the same Phylion Lithium battery 37V 10Ah as old as the Torq - two different bikes/riders - similar terrain.
Bike No:1 - A torq New July 2006 - 1400 miles.
Rider 67 yo - about 75 kg - pretty fit. 1 charge full to dead (naughty boy) 29 miles varied terrain, undulating some steep (10%).

Bike No: 2 - A sprint New May 2007 - 357 miles.
Rider 77 yo - 90kgs + 2 spare batteries- very unfit. On 1 charge full to nearly dead - (in the interests of science) 21.1 miles similar terrain.

Rider of Bike No: 1 says he always rides his battery to empty (he's a tourist, like me).

I have noticed when riding my Sprint when the power is off there is quite some resistance when pedalling quite unlike the easy going motion of a quality Touring Bike of 28 lbs. It is set up correctly with freely spinning wheels.
Peter

 

[flecc]

They're consistent with each other if the Torq is restricted, which I feel certain it is judging from that range Peter. However, that battery is performing exceptionally well, and it doesn't match the experiences of most others with the eZee Li-ions over one year.

My own experiences in a very hilly area and A to B's in a flatter area have both been different from those. My batteries tend to become unusable due to increased cutting out frequency under steep hill climb load, so there isn't much chance to measure capacity loss. A to B don't get the cutting out too often, due to less hills, but the capacity/range dropped by 35%.

Looking at all four cases and noting the differences in each circumstance highlights how difficult it is to be definitive for everyone, emphasising the importance of interpreting predictions against one's own circumstance and usage.
.

 

[rooel]

Flecc, when you say:

"The worst conditions are using the entire charge every time to empty"

do you really mean down to zero voltage, or do you mean down to the cut-off point set by a circuit board on the battery?

The 18.5 volt Lipo from Poweriser which I am using cuts power to the motor when the no-load voltage across the discharge pins falls to 15 volts (having started at 21.5 volts when fully charged). As there are five cells in the pack this means that the voltage per pack is never allowed to fall below 3volt, which I understand would quickly ruin the pack.

This, together with the fact that the Sram Sparc with its efficient, but low power motors which never draw a peak amperage any where near the 40 amps which the Poweriser Lipo can provide gives me some hope that this battery will remain in good condition for a long time.

 

[flecc]

No, always only down to the cut-off point Rooel.

This is always my meaning on all batteries in the forum, since they all are system protected by charger or motor controller.

I hope that is the case for your battery, but most expert opinion isn't promising and experience so far has been poor.

Some battery technical people and all the manufacturers are just refusing to see the evidence, adopting a three monkeys strategy, see no evil, hear no evil, speak no evil.

On usage, one after another they trot out the same story, "our battery can deliver 20 Amps continuous so there cannot be a problem with your motor", lab test results of course. The problem they refuse to acknowledge is that under the high load of a powerful motor, these cells tire, the voltage drops below 32 volts and then safety cut-out operates. We know that because it happens to all those of us with the most powerful motors, proving that those batteries drop under load to delivering less than 16 Amps.

On life, they insist that there will still be 70% capacity after 2 years. Battery experts predict that they lose 33% per annum, and the first to arrive at a year old have indeed been about 33 to 35% down. Therefore, far from that 70% being left at 2 years, it's more likely that's the amount lost after 2 years.

That's for those in flat areas (so less load stress) who still have them working! In hillier conditions, my first one was useless and exchanged at 6 months, the second has lasted on a more economical bike to 11 months and now scrapped, and the third has just started cutting out at nearly 7 months, and will be useless in the colder winter weather. Not promising at £250 each is it?

The one thing you've got going for you is that your Sparc is a lower powered system so will stress the cells less. Also, if your area is not very hilly, that will also give a longer life. That said, I'd treat that claim of 40 Amps with suspicion in the light of experience with our so called 20 Amp batteries. Your Lipos would probably only sustain 28 Amps tops for long hill climbs, but for your motor of course, that's more than enough with plenty of safety margin.

But you can see why so many of us are completely fed up with Li-ion in all it's forms and want suppliers to return to NiMh, which works, until they do get Li-ion right, if ever. If they carry on as they are without drastic improvement, they'll go out of business since people just won't stand for it.
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[coops]

I must be either getting more risk averse, or just less willing to "splash out", but I'm so glad now I took your advice to go for NiMH as a less risky option, flecc, despite my local area being mostly not hilly. Saved myself around £100 too .

Stuart.

 

[flecc]

I'll be in the market for another battery before next winter Stuart, but see the eZee NiMh is up to £190 now, when available. Getting closer to Li-ion, but still much cheaper if life is taken into account. I just wish their charger had a refresh discharger built in though.
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[coops]

EDIT: posted questions to be moved to NiMH FAQ thread, if unasked there .

Stuart.

 

[FatMog]

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.
.

That's me! I knew this before I bought my sprint this spring cos it'd all been explained to me by this site. So I hope to get two to three years out of my battery, but forwarned is forarmed and I stick a tenner (literally!) in my 'new battery' piggy bank every month to make the inevitable more palatable when the time comes!

 

[deesee]

Li-ion against Ni-MH

It's good to get batteries clear. They are, after all, literally the Power House of an electric bike. I recently tried out the Ezee Forte with Tim Snaith (of 50cycles) at his address in Bayswater. I asked him whether it was possible to have a Ni-MH battery instead of Li-ion which the bike is advertised as having. The answer was yes.

I'm still thinking about buying a Forte or Forza and, if I do take the plunge, I shall certainly go for the Ni-MH option.

David

 

[Ian]

That's good news Deesee, not only for new purchasers but also for Ezee NiMh owners requiring replacements and those wishing to "upgrade" from Li to NiMh.
As a point of interest I gave my 1 year old NiMh battery a periodic conditioning discharge yesterday (I have an old charger that can do that), and in doing so found it's capacity to still be slightly higher than specified.

FatMog, yours is a very sensible policy, having realistic expectations will avoid disappointment when your battery does fail and owning a reputable brand will ensure a replacement is available. It's a pity that many manufacturers/suppliers continue to make hopelessly unrealistic claims about what the customer can expect in terms of life.

 

[bersh]

red yellow green

I am new to this blog. I purchased a Quando II in June of 2007. Its LI Battery is now back at the dealer and the testing is not yet finished, but will be later today. So far, I was informed that using the dealer's charge and test equipment, the numbers are 8.5 out of 10 which represents a 5 percent loss of storage capacity. Since I had recharged the battery only 6 times with 80 per cent of distance traveled flat, but the 20 percent remaining on fairly steep San Francisco hills, I am concerned that there will be only 150 charges left. The technician stated that at the point of my phone call, testing on my charger indicated a possible defect on that charger. My experience on that charger (it came with the battery and bike) was a fairly rapid decline in length between recharges and thus a sense that the battery was rapidly losing capacity and would never make more than one year. The owner of the store from which I purchased it, upon my returning the battery for testing, stated that I should recharge it after every use. He never said that at the time I bought it, or the times that I spoke with him on the phone in the first two months of usage. But most troubling is that the instruction manual does not really define deep discharge, and even worse, does not correlate red, yellow and green light display with when to recharge. Would all of you please relate your experiences with this? Thanks from Bersh ps, the warranty is still very much in play. I really want the vendor to give me a new battery and a new recharger...and maybe I should try to get the NIMH instead of LI, although it is not clear whether that is an option...and finally, could the recharger given be the wrong one, ie, engineered for NIMH but not LI?

 

[flecc]

The Chargers are clearly labelled for Li-ion or NiMh Bersch, so if labelled correctly your's should be ok. You can check this though. If you measure witha meter the voltage the charger gives when switched on, the Li-ion charger gives about 41.4 volts, the NiMh charger about 53 volts, so you can see there's no mistaking which is which. If you do this, it's very easy to short to the XLR plug case as you probe, so please insert a loop of paper strip into the plug housing first so your meter probes cannot short a pin to the plug casing and short the charger. The outer two pins carry those voltages, the middle pin unused on Li-ion chargers.

These battery meters only give an accurate reading if stationary or if the throttle is shut off, at other times the current being used by the motor distorts the reading.

With Li-ion it's always best to charge as often as possible, the shorter the distances between charges the better. A part charge doesn't count as a full charge in the estimate of the number of charges they will stand, and I stress that is an estimate anyway since there's little accumulated knowledge of high capacity Lithium traction batteries yet. Some labs say 400 charges, most 500, but some insist 800 full charges, so we'll just have to wait and see.

Under very high loads such as when climbing long or steep hills, these batteries can cut-out for safety reasons, and a switch off and on is then necessary to reset them. If your riding conditions cause this kind of cut-out frequently, that shortens the life in my experience, but for most this isn't a problem.

The Liv works equally well with an NiMh battery if you can get them, and they are rather different in that they should be discharged to the bike cut off point one every so often, about every 10 charges or monthly whichever is sooner, but the exact frequency isn't critical.
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[4beeches0]

Hi Flecc

Having just bought a new Liv yesterday, with which I am generally very pleased, I was concerned to read the posts relating to Li-ion battery life. I understand that I should run the battery to flat for the first two or three times and then resort to frequent charges after every run. I was heartened to hear that a NiMH battery can be fitted to the Liv - is this without modification to the bike and could I expect similar range ? My cycling is usually on fairly flat terrain short single figure journeys two or three times a week with an occasional run of aprox 20 miles. Maybe my best bet is to continue using my Li-ion and switch to NiMH when performance starts to fall away. Any thoughts you may have on this situation would be appreciated.

John

 

[flecc]

Hello John. Li-ion batteries age continuously regardless of whether they are used or not, so it's best now to continue with the Li-ion until it's no more use to you. Just charge every run and you'll get the best you can out of it.

Every eZee models except the Forza and Forte were designed and marketed with NiMh batteries, the Li-ion introduced later as a retrofit. Indeed the Liv was NiMh only until a shortage of nickel and batteries in consequence forced the switch to Li-ion. Therefore they are freely interchangeable.

I'm using up a Li-ion on my main eZee bike until it's had it, but switch to an NiMh for trailer towing trips since the Li-ion isn't up to that.
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[4beeches0]

Hello Flecc Thanks for your advice on Li-ion battery. On my new Liv I achieved aprox 15 miles on the first charge, on my second charge the orange light started coming on at only 10 miles and rather than get an improvement over my first charge I fear it may not be as good. To be honest I was hoping to achieve a minimum of 20 miles on a charge. Is it likely that I would do better with a NiMH battery ? If so I could use the Li-ion for short local journeys and the NiMH for longer runs. I live aprox 10 miles from York and was hoping I could achieve the round trip on one charge - I am beginning to doubt that this will be possible with my Li-ion battery. Not too keen on having to fork out another £250 for battery and charger but I do want to get this sorted.

John

 

[UrbanPuma]

Hi 4beeches0,

Do you ride in pedal assist mode or use throttle only when you use the bike?

 

[4beeches0]

Hi UrbanPuma

Always ride in pedal assist mode feeding the power in in a very miserly fashion in order to gain maximum mileage. All my journeys are on relatively flat roads, slight inclines but certainly no energy sapping hills to contend with. On my last bike, a cheap Chinese import using NiMH batteries average mileage per charge was 15 to 16. I was hoping for better things with my new higher specced Liv and Li-ion batteries.

John