What counts as a charge?

[torrent99]

Folks,

When you look at the descriptions of battery life the number of charges per lifetime e.g. 500 charges is quoted.

But what counts as a charge? Is it full cycle from flat to full? Or does every top up charge count i.e. every charge after a short journey?

Cheers

Steve

 

[flecc]

500 full charges Steve. It's debatable exactly how that relates to part charges since they can be so variable, but with some common sense it should be roughly pro rata. By that I mean not doing part charges after a mile or two of use but using at least a reasonable proportion of the content first, at least a quarter to a third.

The points of greatest strain on the battery cells is at full discharge and full charge, so avoiding full discharge and applying some moderation to the number of occasions of full charge will give the longest life. If you could operate between 30% and 80% of charge it would be ideal, but that's difficult to arrange during charging as there's no certainty of what's in the battery. The best systems usually cut the charge early enough to avoid undue stress though, so leaving that to the charger design is sufficient for normal purposes.

In any event, the 500 charges figure is nominal, indicated by laboratory testing as likely, but the actual figure will vary according to a wide range of conditions, operating temperatures, amounts of discharge, charge frequency, discharge rates and many others.
.

 

[JamesC]

500 full charges Steve. It's debatable exactly how that relates to part charges since they can be so variable, but with some common sense it should be roughly pro rata. By that I mean not doing part charges after a mile or two of use but using at least a reasonable proportion of the content first, at least a quarter to a third.

The points of greatest strain on the battery cells is at full discharge and full charge, so avoiding full discharge and applying some moderation to the number of occasions of full charge will give the longest life. If you could operate between 30% and 80% of charge it would be ideal, but that's difficult to arrange during charging as there's no certainty of what's in the battery. The best systems usually cut the charge early enough to avoid undue stress though, so leaving that to the charger design is sufficient for normal purposes.

In any event, the 500 charges figure is nominal, indicated by laboratory testing as likely, but the actual figure will vary according to a wide range of conditions, operating temperatures, amounts of discharge, charge frequency, discharge rates and many others.
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Flecc
I remember an interesting post from kreuterbutter, largely based on his experience with model aeroplane batteries.

He is a big believer in charging the battery just prior to use, and not just doing it willynilly immediately after use.

His view was that leaving the battery in a fully charged state without using the bike for a few days (weather or whatever), was an unneccessary stress on the battery.

I would tend to be guilty of this, not always being 100% certain when I will next need the bike.

Over the course of a year, I imagine there could be at least 2 days per week when the batteries are charged and I don't use the bike - probably more than 100 days in the year.

Would it be better to charge prior to needing it (if I became more organised !!) ?

James

 

[torrent99]

500 full charges Steve. It's debatable exactly how that relates to part charges since they can be so variable, but with some common sense it should be roughly pro rata. By that I mean not doing part charges after a mile or two of use but using at least a reasonable proportion of the content first, at least a quarter to a third.
.

So just to clarify (I like things in really simple language!), if you do 4 quarter charges that adds up to a full charge?

I suppose my next question is, do we know in real life what that 500 charge figure typically turns out to mean?
(I'm thinking here of a use scenario where the bike is run for shorter (say 20% of the "range") journeys and topped up between journeys.)

Cheers

Steve

 

[Barnowl]

So just to clarify (I like things in really simple language!), if you do 4 quarter charges that adds up to a full charge?

I suppose my next question is, do we know in real life what that 500 charge figure typically turns out to mean?
(I'm thinking here of a use scenario where the bike is run for shorter (say 20% of the "range") journeys and topped up between journeys.)

Cheers

Steve

Interesting. I keep a rough record of my charges and count them typically as 1/3 or 2/3 or full charge.
I can just about get 3 days commuting out of my battery but usually recharge on the 3rd day (hence I log a 2/3 charge). Avoids stressing the battery as well. Most weekends I usually do a run that almost drains the battery and I count that recharge as a full charge.
Personally I'd total the lot and say that was the number of charges ie 1/3 charge +2/3 charge + 1 charge = 2 charges.
Not exact science I know but at least it gives me a rough idea.

 

[flecc]

Yes, four quarter charges equals one full charge Steve. In practice I think 500 full charges will prove to be a best figure for most lithium based batteries, judging from experience to date, but much depends on the range needed.

For example, if I use a bike chiefly for 4 mile shopping trips in a fairly flat area, I might still be able to do one of those on a battery over three years old which had been through over 500 charges, but that battery would be useless for a commuter who wanted to cover 15 miles each way with some steep hills. That commuter might well have had to scrap the battery at before 400 charges even.

What I'm emphasizing here is that batteries in well managed bike systems don't just stop working suddenly, they merely gradually deteriorate in both range and peak outputs.

James, I remember kraeuterbutter's comments on that, but I'm not confident that the conditions applying to small LiFePO4 cells hold true for other and larger types, the cathode and chemistry differences being very real. I think the better bike charging systems are good enough for our purposes to stop charging sufficiently short of absolute maximum.

That said, it's always best to charge just before use where possible for best performance, but the real cell stress is experienced during the last 10% of charge as current actually flows into the cells against growing resistance, generating heat. Once charged and off current, the chemical state is stable with heat going quickly and any ill effect will be minimal compared with the actual period of late charge.
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[JamesC]

James, I remember kraeuterbutter's comments on that, but I'm not confident that the conditions applying to small LiFePO4 cells hold true for other and larger types, the cathode and chemistry differences being very real. I think the better bike charging systems are good enough for our purposes to stop charging sufficiently short of absolute maximum.

That said, it's always best to charge just before use where possible for best performance, but the real cell stress is experienced during the last 10% of charge as current actually flows into the cells against growing resistance, generating heat. Once charged and off current, the chemical state is stable with heat going quickly and any ill effect will be minimal compared with the actual period of late charge.

Thanks Flecc - I can see the stress of squeezing in the final stage of the charge.

James

PS Sorry Flecc - I rubbed out the Size references - How do you set them up ?

 

[flecc]

PS Sorry Flecc - I rubbed out the Size references - How do you set them up ?

I just type the part needed, say LiFePO

and at that point I select "1" from the text sizes reference box at the top of the reply box. I then type the 4 thus, immediately returning the size box to 2 again afterwards as I've done here. When you select the "Edit" facility, you won't see the text size box unless you select "Go Advanced" first.
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[flecc]

P.S. James.

You may see things differently from me in your reply boxes in this site if you are using the default mode like most members.

If, like me, you'd like to see the reply box in full WYSIWYG mode (what you see is what you get) and your computer us fairly fast, go to the Quick Links above and select "Edit Options". Then scroll down to the Message Editor Interface and select:

Enhanced Interface - Full WYSIWIG editing
in the drop down box.

You'll then get an effectively "live" view of your input before entering it, though when editing subsequently that only appears when Advanced View is selected.
.

 

[Danny-K]

. . . largely based on his experience with model aeroplane batteries.

He is a big believer in charging the battery just prior to use, and not just doing it willynilly immediately after use.

His view was that leaving the battery in a fully charged state without using the bike for a few days (weather or whatever), was an unnecessary stress on the battery.

Purely subjectively - I'd swear there was something to that theory. Normally I get 27 trouble free miles to the charge out of my battery, (it's 6 months old). Recently, I had occasion to leave the bike in the garage for nigh on 5 days, (I'm not a commuter), and when I came to use the battery (stored indoors), which had been charged 'willynilly immediately after the last run', to my surprise the first red light went out in half the usual mileage, finally the last light was left on its lonesome about three quarters it's usual expiry mileage - so back home I immediately recharged - which is another point: I tend to travel regular distances in one go that reach the limits of my battery's endurance in one swoop. So I guess I'm an 80% to 100% depletion man. I must be a cruel battery man.

From now on, I'm going to make a determined effort to charge just before usage to see if the above assumption 'holds any water'. I've noticed this early depletion before - when the charged-up battery had been sitting for several days before usage. It's probably pure coincidence and more to do with usage in the freezing cold weather, but . . . hmmm . . . if I can plan-in a choice of either immediate charging or charging just prior to travelling . . .

 

[flecc]

Actually lithium-ion cells don't have any self discharge, this toted as a big advantage when these were first promoted, so charge loss due to that or when charged is ruled out. Losses result in complete battery assemblies due to the interconnected protection and charge control electronics, but those will be at a fairly constant rate regardless of when charged. Some BMS protection circuitry may be greedier than others which might give variations between makes.
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[torrent99]

A battery regime for commuters...

So, putting together stuff from various threads old and current. If we were to devise a battery charging regime for commuters it might go along the lines of:


A) Get a bigger battery than you "need" to get the range (preferably much bigger). At least add a few Ah for comfort. Why? So you avoid doing deep discharge.

B) Attempt to only charge to 80% of full for most charges. How?
Here's a guess.
1) Charge to full.
2) Do the journey.
3) Recharge to full but time how long it takes.
4) Do the journey
5) Recharge for 80-90% of the time noted in 3.
6) Do the journey.
7) Charge for the full time noted in 3. i.e. 80-90%
8) Repeat 6 &7 for say 5 times (or maybe the remainder of the week)
7) Go back to step 3.

Of course this only works for people like commuters who have a predictable journey every day, and even then factors like traffic mean that it's not going to be completly accurate. (Hence the regular full recharge and re-time)


C) Store and if poss. charge the battery outside where it's colder.

D) Store the battery in the fridge at the weekend.


Complicated isn't it!? The question is would it work?



Cheers

Steve

 

[Barnowl]

Speaking as a kindly 60 - 90% man, I always charge mine immediately before a run - usually while I'm getting ready for work. It only takes about an hour (NIMH) so my "thermos flask" is nice and warm(ish) when I start off. Seems to work well because I haven't noticed any problems.
I have to say I don't have any battery indicator so the state of the battery is not something I'm made aware of. Maybe they can be a mixed blessing.
As long as the assistance is always there I don't much care. I haven't ran out of charge since I first recycled the battery.
I guess battery performance really becomes an issue when you're challenging the distance and speed boundaries. Be kind to batteries - you know it makes sense cos they ain't cheap!.

 

[Barnowl]

A) Get a bigger battery than you "need" to get the range (preferably much bigger). At least add a few Ah for comfort. Why? So you avoid doing deep discharge.

B) Attempt to only charge to 80% of full for most charges. How?
Here's a guess.
1) Charge to full.
2) Do the journey.
3) Recharge to full but time how long it takes.
4) Do the journey
5) Recharge for 80-90% of the time noted in 3.
6) Do the journey.
7) Charge for the full time noted in 3. i.e. 80-90%
8) Repeat 6 &7 for say 5 times (or maybe the remainder of the week)
7) Go back to step 3.

Of course this only works for people like commuters who have a predictable journey every day, and even then factors like traffic mean that it's not going to be completly accurate. (Hence the regular full recharge and re-time)


C) Store and if poss. charge the battery outside where it's colder.

D) Store the battery in the fridge at the weekend.


Complicated isn't it!? The question is would it work?



Cheers

Steve

A) Yes. You need to allow for a drop in performance later in battery life
B) Don't bother. It's not easy to time (I tried it) and it's not worth the hassle. A good charger should allow for this and cut out.
C) No. Store indoors. The cold (in winter) will have a detrimental effect on battery performance.
D) No way! My fridge is too small! Also see C)

No I don't think it's complicated. Just keep a check on your mileage and recharge before the battery runs out. Keep the battery indoors and that's it.

 

[flecc]

C) Store and if poss. charge the battery outside where it's colder.

D) Store the battery in the fridge at the weekend.

A and B are fine Steve, but C and D questionable.

C) Storing the battery outside is only viable down to zero degrees C since they must not be frozen, and will give lousy morning performance anyway, so definitely not worth it. In addition, charging should never be done at low temperatures as it reduces the amount of charge the battery can take up. Remember it's a chemical reaction which as always needs heat. In general batteries function best in all modes at 20 to 30 degrees C, so best move to California.

D) Cold storage at weekends is far too short to gain and anyway theres no gain if fully charged. Cold storage between zero and 5 degrees C is only for long term preservation when the charge when stored is between 20 and 40% of full. That reduces the lithium battery capacity loss to as little as 2% per annum, compared with up to 35% at normal temperatures. The saving over weekends is miniscule and will be offset by the frequent temperature change stresses, possibly harming the battery.

Personally, despite being very familiar with all this stuff, I just use my bike batteries and get new ones when necessary, not bothering with all the palaver. The only battery that gets special treatment is my laptop one which I only use two or three times a year, so that lives wrapped in clingfilm at back of the bottom shelf of the fridge at about 40% charge at all other times.
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[torrent99]

A) Yes. You need to allow for a drop in performance later in battery life
B) Don't bother. It's not easy to time (I tried it) and it's not worth the hassle. A good charger should allow for this and cut out.
C) No. Store indoors. The cold (in winter) will have a detrimental effect on battery performance.
D) No way! My fridge is too small! Also see C)

No I don't think it's complicated. Just keep a check on your mileage and recharge before the battery runs out. Keep the battery indoors and that's it.

RE: C) & D) for NiMH storing indoors would be the correct thing to do.

But for LiIon batteries, these degrade over time as a function of temperature and stored charge. Storing at low temperature and partially charged reduces the inherent degredation of the cell e.g. at 0degrees C and 40% charge degredation is around 2% per annum, whilst at 25 degrees and 100% charge it's around 20% (source www.batteryuniversity.com). So storing LiIon batteries somewhere cool and partially discharged makes sense. Charge inside, but store outside (or in the fridge!).

 

[Barnowl]

RE: C) & D) for NiMH storing indoors would be the correct thing to do.

But for LiIon batteries, these degrade over time as a function of temperature and stored charge. Storing at low temperature and partially charged reduces the inherent degredation of the cell e.g. at 0degrees C and 40% charge degredation is around 2% per annum, whilst at 25 degrees and 100% charge it's around 20% (source www.batteryuniversity.com). So storing LiIon batteries somewhere cool and partially discharged makes sense. Charge inside, but store outside (or in the fridge!).

Thanks torrent99, I hadn't appreciated that difference between Lithium ion and NIMH. As NIMH is going out of fashion, I guess at some point in the future, I will end up with a Lithium battery of some flavour. Hopefully I'm several years away from that.
Crikey my wife would kill me if I tried to store a bike battery in the fridge! Also I use my bike at weekends so wouldn't (hypothetically) be worth the effort. Good idea for serious long term storage though.

 

[flecc]

RE: C) & D) for NiMH storing indoors would be the correct thing to do.

But for LiIon batteries, these degrade over time as a function of temperature and stored charge. Storing at low temperature and partially charged reduces the inherent degredation of the cell e.g. at 0degrees C and 40% charge degredation is around 2% per annum, whilst at 25 degrees and 100% charge it's around 20% (source www.batteryuniversity.com). So storing LiIon batteries somewhere cool and partially discharged makes sense. Charge inside, but store outside (or in the fridge!).

But not worth it short term like weekends Steve. To get a decent following performance you'll need to bring it back up to temperature before recharging and that takes some hours, while at the start of the weekend it will take hours to get down to a low temperature, which will often be well above zero degrees usually anyway. Even fridges are rarely at zero degrees, 5 to 10 degrees C being more commonplace, which raises the capacity loss well above 2% per annum. Add in the regular temperature change stresses imposed and you'd probably lose as much as you gained. The Battery University information is specifically for long term storage, which is why they quote annual capacity loss figures.
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[torrent99]

But not worth it short term like weekends Steve. To get a decent following performance you'll need to bring it back up to temperature before recharging and that takes some hours, while at the start of the weekend it will take hours to get down to a low temperature, which will often be well above zero degrees usually anyway. Even fridges are rarely at zero degrees, 5 to 10 degrees C being more commonplace, which raises the capacity loss well above 2% per annum. Add in the regular temperature change stresses imposed and you'd probably lose as much as you gained. The Battery University information is specifically for long term storage, which is why they quote annual capacity loss figures.
.

Ah... I didn't realise there was a thermal stress component as well! I suppose there's probably an ideal compromise temperature to charge and store at, but it's likely to be too difficult to determine. Interestingly I found on Wikipedia (not necessarily the best source I know!):
"Li-ion batteries should not be frozen [39] (most lithium-ion battery electrolytes freeze at approximately −40 °C; however, this is much colder than the lowest temperature reached by household freezers). "



So anyway the list becomes:
A) Get a bigger battery than you need, both to have capacity in reserve for annual degredation, and to reduce the size of the cycling.

The other idea I'm interested in is Nick(Tiberius)'s add on battery pack, where he attached 2 small NiMH packs in parallel with his main LiIon. The concept of mixing battery chemistries so you play to each of their strengths is very appealing, and in Nick's case it appeared to show ability to eek out the life of a marginal LiIon.

I can see the possiblity of having different ratios of chemistries depending on the likely terrain on the user. Far too complex for commercial consumer applications though. But for e-bike Formula 1...

 

[flecc]

Bigger battery is always a good solution, solving several problems in one.

As a matter of interest I did a tot up yesterday of the benefit of fridge storage at weekends, allowing for cooling time for the entire content at the outset, full warm up and charge time at the end on each occasion, and assuming no thermal stress effects.

Based on a bike doing around 20/25 miles range and a normal capacity loss of around 20% per annum, I calculated that the range would be extended at the end of the first year by around 0.9 miles at best if the temperature of the fridge really was at around zero degrees C constant. Since it would much more likely be around 5 degrees C average with some thermal stress inevitable the range gain would probably be more like half that. Taking that into account and all the hassle involved in the cooling and charging procedures, I think it's shown it wouldn't be worthwhile for such a miserly gain.
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