Some advices to STORE YOUR BATTERY for the winter period

Batteries, Chargers, and Battery Management Systems.
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Doctorbass   100 GW

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Some advices to STORE YOUR BATTERY for the winter period

Post by Doctorbass » Nov 26 2008 9:42pm

For some of us, the winter season is at our doors and some of us will store theor ebike for few months,

I though that it could be good for you to know some great advices about this and you lithium ion battery.

That mostly concern peoples that store their bike for couples of months for that cold season.

I'm sure that many of us already heard that keeping a battery fully charged will help to keep it's long life and prevent loosing capacity and other dammages. This is particularrly thru with SLA and most of the NiCad battery.

But!.. for the lithium this is something different!!

Lithium cells will not lose the same amount of charge like sla and nicad do.


Here is what is HIGHLY remommanded:

0-Avoid to keep them at 4.20V or 3.7V(LiFePO4) for a long period and in a warm or hot environment!!

1-Store your battery to around 40-50%state of charge (generally it's equivalent to 3.7-3.8V per cells for the normal 4.2V 100%soc lithium for the A123 / LiFePO4 is different and it's 3.05-3.10V

2- Store them in a cold area. Usually around 15 degreeC is perfect but below 25 degreeC and above freezing point.

3-If stored for more than one years.. (it's a rare situation for us i guess...) One a year, fully charge them to 4.2V or 3.7V(for LiFePO4) and then discharge them to their storage voltage mintionned above.

4- Ensure that they will never go below 2.5V during this period.

Here is some references about that: http://www.batteryuniversity.com/parttwo-34.htm

Doc
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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by steveo » Nov 27 2008 12:43am

nice aid!

crap.. this means i have to burn sum ah in my house to bring the voltages down lol .. or bring the bike for a nice run. :D

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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by Mr. Mik » Nov 27 2008 7:17pm

What happens when the Li cells are stored fully charged?
Mr. Mik

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The writer of this post accepts no responsibility or liability resulting from attempts to repeat or perform the procedures described in this post. This information may be used at your own risk.

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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by Doctorbass » Nov 27 2008 7:48pm

Mr. Mik wrote:What happens when the Li cells are stored fully charged?
Their life will be shortened.
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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by swbluto » Nov 27 2008 8:38pm

Hmmmmm... I wonder by what percentage for both cycle life and calendar life. I imagine that storing it fully charged may reduce its calendar life by 20-50%, but if it's used 200 cycles a year and it would have had a 1000 cycle life otherwise but instead now has a 900 cycle life, then that's only a 10% reduction in the cycle life. Surely there's some mathematical relationship between cycle life and calendar life degradation.

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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by Doctorbass » Nov 27 2008 9:25pm

If you CAREFULLY read the link to the battery university that i posted on top, you will find this:


Figure 1: Permanent capacity loss of lithium-ion as a function of temperature and charge level.
High charge levels and elevated temperatures hasten permanent capacity loss. Improvements in chemistry have increased the storage performance of lithium-ion batteries
Image

and another important thing to remember about laptop!!:
The worst condition is keeping a fully charged battery at elevated temperatures, which is the case with running laptop batteries. If used on main power, the battery inside a laptop will only last for 12-18 months.

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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by swbluto » Nov 27 2008 9:44pm

I saw the relationship for calendar life but not for cycle life, and a battery's "cycle life" and "calendar life" is not a 1-to-1 correspondence. Since I have a feeling many of the ping users are going to deplete their battery capacity by cycle use rather than desuetude, this is kind of an important thing to know.

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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by ZapPat » Nov 28 2008 7:31am

Good info, Doc!

These numbers are for Lithium cobalt cells, right? LiFePO4 will have less loss of capacity (in percentage)than LiCo, but the 100% charged vs 40% charged capacity loss ratio should still be similar, right? What this also means is that avoiding charging your batt to 100% will extend it's life, as long as balancing is done once in a while.

Oh boy... one more potentialy very interesting long-term test to be added to the "cell testing wishlist"! :shock:

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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by ejonesss » Nov 28 2008 2:24pm

is this apply to lifepo4 too?



Doctorbass wrote:
Mr. Mik wrote:What happens when the Li cells are stored fully charged?
Their life will be shortened.
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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by Doctorbass » Nov 28 2008 5:22pm

ZapPat wrote:Good info, Doc!

These numbers are for Lithium cobalt cells, right? LiFePO4 will have less loss of capacity (in percentage)than LiCo, but the 100% charged vs 40% charged capacity loss ratio should still be similar, right? What this also means is that avoiding charging your batt to 100% will extend it's life, as long as balancing is done once in a while.

Oh boy... one more potentialy very interesting long-term test to be added to the "cell testing wishlist"! :shock:
The principle is the same for the liFePO4 but the effect is less important on them. I have no numbers to give and they are difficult to find between these two kind lithium cells.

The principle always concern the INTERNAL heat of the cell AND the chemical reaction coming from the high voltage state for long period storage.

These are the main cause of stress that lithium cells have.

Most of people think it's high current is the cause... but this is secondary effect only.. cause high current will create HEAT if the cell have high internal resistance. and high resistance occur also when cells havelost capacity over calandar life.. andalso when approaching low or high voltage cutoff..


Doc
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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by powermed » Nov 28 2008 5:54pm

Excellent advice. Another thing to keep in mind is that any attached device - such as a charger or DC converter may have a slight amp draw. Over time it can be enough to ruin a battery. If in doubt it's best to disconnect them entirely!
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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by dak664 » Nov 29 2008 8:40am

If LiIon batteries deteriorate more slowly when half charged, then wouldn't it be better to delay charging until the battery is needed, even if only overnight? And wouldn't a slower charge be better, since the battery would spend more time at less than full? A slow charge would mean a lower temperature and be easier on the BMS too. How about a smart controller that lets you set when you need the battery next, and it figures out the best parameters for battery life, and delivers a fully charged battery just in time?

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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by Doctorbass » Nov 30 2008 12:36pm

dak664 wrote:If LiIon batteries deteriorate more slowly when half charged, then wouldn't it be better to delay charging until the battery is needed, even if only overnight? . How about a smart controller that lets you set when you need the battery next, and it figures out the best parameters for battery life, and delivers a fully charged battery just in time?

That's an excellent question!
wouldn't it be better to delay charging until the battery is needed, even if only overnight?
Yes, that is the better way. But you will need to plan when you will need your battery and sometimes it's too much work for doing simple quick ride... the capacity lost over the time would represent like 5-10% over the total life.. so it depend how you want to profit of your ebike..

Planning every use of it and charging it overnight just before the use and having a gain of 5-10% more life of your batery... well.. it depend how you pecieve that...

Some people will want to have their bike ready for every ride.. some not..
And wouldn't a slower charge be better, since the battery would spend more time at less than full? A slow charge would mean a lower temperature and be easier on the BMS too
Certainly, a slower charge is always better cause the current that travel the cell is lower and will generate less heat inside it and will let the BMS to do a better work!.. and then.. encourage a very long battery life.

How about a smart controller that lets you set when you need the battery next, and it figures out the best parameters for battery life, and delivers a fully charged battery just in time?
That's a great idea.. i think i've heard of some EV home charger working like that... but again like i said a great and accurate planning of the future use of your ev will be a must!

Doc
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Re: Some advices to STORE YOUR BATTERY for the winter period

Post by totals » Dec 24 2008 8:04pm

I have a simple answer for the daily rider looking for just in time chargin.

I bought a wall timer that you can program to turn on as needed.

My battery fully charges in 3 to 4 hours tops. I leave my place at 8 in the morning. So, the night before, I plug my bike in and the timer doesn't turn on until 4am, then charges up the bike, which is then ready to go by 8am.

I posted a video to show you what I mean here: http://www.youtube.com/watch?v=RJAezKY9m6g

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