Battery problem - Help!

[UrbanPuma]

Hi all,

I recently rode my bike (powacycle puma) after some months left unused and only acheived 6 miles. I accept the fact that lithium batteries loose charge after some time regardless of them being used or not. After my last ride, the battery was completely empty and i did not charge it until a couple of days later. I've now just tried to used the bike and i am not receiving any lights on the battery indicator or the power display. When I connect the battery to the charger in it shows a green light indicating the battery is charged.

Anyone know whats wrong?

 

[BMI]

Sounds like you have one or more faulty cells. You need to be able to load test each and every cell in the pack to find where the defective cells are. It may be only one cell which is defective or several but you need to be able to get access to each of the individual cell's terminals to be able to test them.

 

[UrbanPuma]

Hi BMI,

I'm not technically minded at all and wouldnt know where to start with regards to checking the cells in the battery. Is there anything i can do to revive the battery or should i just take it to a shop? I used to get 16 miles per charge at the beginning, then i left the bike in storage for approx 7 months without charging it. Ony returned to using it recently and was only getting 6 miles from the battery.

Do you think the battery is nearing the end of its life as ive had the bike since Sept 2007?

 

[flecc]

Leaving it without charge for 7 months was fatal. Lithium-ion batteries need to be charged at least every three months whether used or not, and preferably a bit more frequently. I've a number of small lithium batteries as old as ten years and maintain a charge log, recharging all of them every two months which has kept them going.

There's almost certainly nothing that can be done for that battery now, and I'm surprised you even got 6 miles from it after that time. In fact it would be nearing the end of life at two years anyway, so you haven't lost out too heavily.

There are the odd sophisticated types now that have a sleep mode which enables them to shut down and not deteriorate after a longish period of not being used, the Panasonic battery on bikes like the Kalkhoff being the only one of those I know of on bikes. Sadly your's isn't one of them.

Fortunately a new one for your bike isn't one of the £400 to £500 ones common now, it's currently £249 plus £10 P & P.
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[UrbanPuma]

Hi Flecc,

I thought a new battery would be my only option now I guess this was a very expensive lesson, so i shall be saving up for a new battery, not sure how long that will take lol Are you sure there is absolutely no way i can revive the battery, even to get the 6 miles back?

 

[flecc]

There's no recommended way to do that, all the industry views are that Li-ion cells left uncharged for over about three months are likely to fail completely. If you had recharged first before riding that six miles after the downtime, the chances might have been slightly better, but still not good at all.

When in good condition they can be stored at very low temperature with a part charge in them to make them last. One experimental thing you could try since yours is a small battery, put it in the fridge low down at the back for a couple of days to get thoroughly chilled right through. Then remove it and try starting the charge at various points as it warms up again. I've never tried this and it's a very long shot, but it might just get to a cell chemical state where it can accept some charge.
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[UrbanPuma]

Ok, i will give it a try and report back. Thanks

 

[UrbanPuma]

Flecc, could i try putting it in the freezer instead?

 

[flecc]

No, that would destroy the cells. They are safe down to zero degrees C, but not below. The fridge at around 5 degrees C is completely safe.
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[UrbanPuma]

Ok. Cheers!

 

[BMI]

Gentlemen, we have to be clear which family of lithium ion batteries we are talking about when we discuss self discharge and low temperature performance.
What flecc says is true of lithium ion batteries ie, Li-Co chemistry, as used in consumer appliances such as mobile phones, camcorders, etc but is definitely not true of Lithium Iron Phosphate batteries (LiFePO4). One of the great advantages of LiFePO4 batteries is that they have a very low self discharge rate and continue to provide high discharge power in sub zero temperatures.

The fact that they self discharge very slowly and can be stored in a low state of charge for long periods of time without suffering damage is one of their great advantages over lead acid batteries which have a relatively fast self discharge rate and will definitely be damaged if they are allowed to stand in a partially charged state for long periods of time.

For example high quality LiFePO4 batteries which have fully laser welded cases so as to exclude ingress of humidity and atmospheric contamination will still be perfectly good once recharged after quite a few years sitting around not used. Cells in this category are made by companies such as A123 and BMI. These cells when fully charged and left unused at 25 deg. C will still retain a capacity of greater than 80% after 2 years.
Try doing that with a lead acid battery!

 

[flecc]

We do know our battery technology well BMI.

Urban Puma's battery is a lithium polymer type.

In general popular mainstream e-bikes don't use lithium-iron-phosphate yet, but we have long been well aware of their potential advantages.

However, those mainstream manufacturers who have been testing them over the last two years and more are not yet satisfied with the reliability of production ones, and in at least one case, there's agreement between the bike manufacturer and their battery manufacturer that the time for them is not here yet.

Judging by the performance of those supplied to date by Li Ping, and your evident faith in the BMI ones as their agent, it may not be too long now before they reach the mainstream, but no-one is going to take risks after the fires and current delivery failures failures of many batteries with either cobalt and manganese cathodes.

There are as well too many warning signs yet, such as Mitsubishi putting back the launch of their electric version of the i-car for the third year running due to LiFePO4 problems again. Things like that make people nervous.
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[BMI]

flecc I assume you are talking about the Mitsubishi i-Miev?
If this is so the battery used by Mitsubishi in this vehicle is not LiFePO4.

The only safe lithium chemistry is LiFePO4. As you correctly state batteries with cobalt and manganese electrodes are a potential fire hazard.
I would well steer away from any lithium polymer battery for an e-bike application because of the potential fire danger.
Lithium polymer batteries in large format/package sizes are strictly prohibited from shipping by air on passenger aircraft due to the potential fire risk. Not so for LiFePO4 batteries. In fact I supply LiFePO4 batteries to a major hospital which uses the BMI batteries to power critical medical equipment which is used to transport patients from small rural towns who are flown to capital city hospitals by air ambulance. LiFePO4 batteries are the only lithium chemistry battery allowed by the International Air Transport Association Regulations to be used aboard aircraft in a large format/size.

I have seen too many lithium polymer fires for my liking which is why I stay well away from them. Just one example of many cases worldwide of a lithium polymer battery fire on an electric bicycle can bee seen here (in this case from France) Just imagine this smoke in a confined space such as inside a car or in an aircraft cabin. At least on a bike you can get off and away from the fire and the only damage is a burned up bicycle-

mon vélo part en fumée - partie 1

So to all those people who choose to use lithium polymer for anything larger than a radio controlled model aircraft battery application I hope your bike doesn't end up in the same state as that of the poor bike owner in the video!!

 

[flecc]

I'm not referring specifically to M-iev BMI, which is only a generic term that Mitsubishi apply to all their current electric car developments. M-iev is also worn by the Sport concept car for example. As stated, I was referring to the electric version of the existing Mitsubishi i-car which uses LiFePO4 batteries which have been delaying it's launch according to an Autumn 2008 statement. Mitsubishi are also intending to launch another production electric car as well in 2010, based on their Colt model this time but with their in-wheel motors. This Colt based model will initially be only for Japan.

Meanwhile Smart have chosen to use natrium-nickel-chloride batteries in preference to LiFePO4, and the Think car also uses this salt technology in it's "zebra" batteries, both of these with initial batches of cars on the road now.

Now let's have a look at some of the other things you've mentioned. Manganese cathode batteries are not a specific fire risk, which is why these were chosen to replace the cobalt cathode ones which were. The latter when poorly manufactured could cause metallic deposition of lithium from the cathode, which particles could penetrate the insulations and cause the shorts which led to fires. Manganese oxide cathodes are not normally prone to this, but the condition can appear if cells which have failed and dropped to below 1.5 volts are revived by applying pulsed higher voltage inputs with specialised equipment. This emphasizes that the fires you mention are caused by misuse, and I would have no difficulty in causing a LiFePO4 fire by misuse. Any large capacity battery can cause a fire as I'm sure you appreciate.

The airline industry is not a good source of reliable information on a subject like this as they've shown in the past with some eccentric decisions. They understandably play doubly safe in any area where there might be any possible doubt.

Your saying one should steer clear of lithium polymer in any e-bike application is odd indeed, since this is the currently preferred technology of nearly all the bike manufacturers and their battery manufacturers, together with the importers and their agents, in preference to LiFePO4. Few if any companies know more about batteries than Panasonic, and lithium polymer is their chosen bike battery technology. It wouldn't surprise me if LiFePO4 cells eventually become polymer ones and soft cased with further development advances, just as the earlier li-ion types did with technological maturity.

I didn't answer some of the earlier points you made, but will do so now. You rightly claimed very low self discharge on the BMI batteries, but all lithium-ion cells have the same near zero self discharge. It's the differences in BMS that cause higher rates through leakage in most Li-ion batteries, but that's not inevitable as Panasonic have shown with their bike battery (lithium polymer!) which shuts down it's BMS to a minimal standby mode to match that ultra low self discharge rate.

The A123 and other tool batteries use relatively small capacity cells, these much easier to produce successfully. It's when cells are upsized to the much larger capacities that e-bikes require for economic production that problems appear for sound physical and chemical reasons. The very successful Tesla car which uses over 6000 small cells illustrates this well, just as it's over £70,000 cost illustrates why that approach is a dead end. It's with the larger cell variants of LiFePO4 that the e-bike manufacturers have had their testing problems.

Of course parallel series arrays of the smaller cells could be used, but this brings two problems. First the already quite high LiFePO4 price would be elevated for a market where consumers are already outraged by current battery prices. Second, the low self discharge would be partially compromised by the more complex BMS that a parallel series array would require to monitor cell charging.

To conclude, the difference in all the current rechargeable lithium types is merely one of the cathode material. Cobalt was the first that could be used successfully and was above halfway up the short list of suitable elements. The manganese that replaced it for safety reasons was less suitable and lower down the list, hence the problems experienced for some while in getting adequate discharge rates in high power applications.

The top of the list and best of all the elements as a cathode material for lithium-ion batteries is iron as used in your BMI batteries, and after years of development effort we now have it working extremely well in smaller cell sizes. I've no doubt it will take over as the future e-bike battery of choice, but the consensus of the industry is not quite yet.

P.S. I should add that the current li-ion battery cathodes in use on major makes of e-bike are compound ones, typically Nickel-Cobalt-Manganese ones, having better life and high current delivery without fire risks. These seem to be finding favour in the car world too, with Nissan and Mitsubishi also working on them.
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