battery life: better to not fully charge?

[Pastabatman]

I know that keeping batteries stored long-term at full charge is not good for battery life. I've seen recommendations that, for long-term storage, battery charge should be maintained around 50-80%, as storage at full charge puts some kind of strain on the batteries. This got me to thinking that perhaps always charging to 100% for daily use is not optimum either, assuming one doesn't need the full charge for range. I fully charge my EM Evo Cross twice daily, M-F, after discharging down to about 60% on each leg of my commute. Under my circumstances, would it be better to instead charge to, say, 80%?

 

[Ravi Kempaiah]

I know that keeping batteries stored long-term at full charge is not good for battery life. I've seen recommendations that, for long-term storage, battery charge should be maintained around 50-80%, as storage at full charge puts some kind of strain on the batteries. This got me to thinking that perhaps always charging to 100% for daily use is not optimum either, assuming one doesn't need the full charge for range. I fully charge my EM Evo Cross twice daily, M-F, after discharging down to about 60% on each leg of my commute. Under my circumstances, would it better to instead charge to, say, 80%?

Yup I have started doing that with my ST2. I charge it only upto 90%
In a few months I will have some conclusive data to decide if this is worthwhile doing.
Also, what we see as 100% may not be the true 100% capacity. So, I'm checking with the product manager to see how the BMS is designed.

I must say this; I own a Thinkpad Tablet Laptop from 2011 and I charge it only to 80% (Think Power Manager program does this for me)
It stays on the dock 80% of the time and whenever I remove it from the dock, I can use it for 2+ hours easily which I think is great for a 4 yr old laptop.

 

[JoePah]

Yep that's the theory, don't fully charge and don't fully discharge. The Volt for instance is charged to around 85%, and the motor kicks in to charge the battery if it falls below 25% or something, and stops charging around 30% (insane GM politics..haha).

Cellman sells chargers that can be selectively charge to 90-100%.

Personally, batteries are so cheap I want to get maximum range, so i don't care too much about maximizing life.

You can charge to say 90% with a cheap timer and your charger. Just check the battery every 30 minutes during charging, and see how long it takes.. After that just use your timer to set that duration, then use a STOP peg to turn of the charger.

 

[Ravi Kempaiah]

Actually GM Volt is designed to use only 60% of its full capacity.
2015 models come with 17.1 Kwhr battery but useable capacity is 10.5 KWhr.

 

[PowerMe]

batteries are so cheap

If only...

Easy Motion batteries for the EVO line run in the neighborhood of $700+ MSRP.

 

[anoNY]

I have a related question for anyone with technical knowledge:

I have also read that it would be best to neither charge fully nor discharge fully. However, it seems to me that, for a given commute (say 50% of total battery capacity used), if you do not charge fully, then your commute will cause the battery to discharge to a lower level. For example, if I were to charge to 80%, then using 50% of total capacity would bring me down to 30% at the end of my commute. On the other hand, if I charge fully to 100%, then my commute only brings the battery down to 50%.

Is it better to charge fully to 100% and then discharge to 50%, or is it better to charge to 80% and then discharge to 30%?

 

[Ravi Kempaiah]

I have a related question for anyone with technical knowledge:

I have also read that it would be best to neither charge fully nor discharge fully. However, it seems to me that, for a given commute (say 50% of total battery capacity used), if you do not charge fully, then your commute will cause the battery to discharge to a lower level. For example, if I were to charge to 80%, then using 50% of total capacity would bring me down to 30% at the end of my commute. On the other hand, if I charge fully to 100%, then my commute only brings the battery down to 50%.

Is it better to charge fully to 100% and then discharge to 50%, or is it better to charge to 80% and then discharge to 30%?

It's really hard to say without knowing the details of the battery cell specs.
If I were you, I would go from 85-90 to 35-40... actually that's what I have been doing on mine.

 

[anoNY]

It's really hard to say without knowing the details of the battery cell specs.
If I were you, I would go from 85-90 to 35-40... actually that's what I have been doing on mine.

Mine are Headway LiMn. My question is really just theoretical since I have no way to determine SOC at the moment. Do you know of any resources on this subject that might discuss multiple types of battery? In the future I plan to go with LiFePo since it seems the most cost effective and weight is not really a problem (I have large panniers and I weigh 220 so battery weight doesn't have much effect on my ride).

 

[Ravi Kempaiah]

Mine are Headway LiMn. My question is really just theoretical since I have no way to determine SOC at the moment. Do you know of any resources on this subject that might discuss multiple types of battery? In the future I plan to go with LiFePo since it seems the most cost effective and weight is not really a problem (I have large panniers and I weigh 220 so battery weight doesn't have much effect on my ride).

To get a grip on the fundamentals, Battery University is a very good source.

 

[George S.]

http://www.amazon.com/gp/product/B005KBB74M?redirect=true&ref_=kinw_myk_ro_title

Lots of detailed info.

 

[JoePah]

@anoNY I had a A2B Metro with LiMn and abused the battery in every way.. I let it charge overnight, then the next day I would run it until it died.. When the voltage recovered (a dead battery does recover voltage after 30 min), I would run it down until it died again.

I did this for 4.5 years. Would say the last 6 months the range dropped from 75% to 60% and was falling fast.

Just keep the battery between 20-90% and you should maximize life... The reason car makers use a more conservative range is the 10 year warranty they provide.

 

[anoNY]

@anoNY I had a A2B Metro with LiMn and abused the battery in every way.. I let it charge overnight, then the next day I would run it until it died.. When the voltage recovered (a dead battery does recover voltage after 30 min), I would run it down until it died again.

I did this for 4.5 years. Would say the last 6 months the range dropped from 75% to 60% and was falling fast.

Just keep the battery between 20-90% and you should maximize life... The reason car makers use a more conservative range is the 10 year warranty they provide.

Wow, I can only hope to get that kind of longevity. Was this a daily commute or was it more occasional use?

 

[anoNY]

http://www.amazon.com/gp/product/B005KBB74M?redirect=true&ref_=kinw_myk_ro_title

Lots of detailed info.

My wife is signing us up for Prime membership soon, so I should be able to get that one free. Thanks for the heads-up!

 

[BafangFan]

This interview was posted recently (saw it on reddit.com/r/ebikes ). Grin Technologies makes something called a Cycle Satiator, and apparently you can set parameters on how much charge a battery gets. It can also track all sorts of stats. I wanted one until I found out it's $300. My battery is $529, so I'm not sure if it's worth the investment yet.

But about 15-20 minutes into the video is a very detailed discussion about batteries and charging. A lot of caveats - to include that some battery management systems only balance the charge between cells after the battery is charged to 100%.

 

[Pastabatman]

But about 15-20 minutes into the video is a very detailed discussion about batteries and charging. A lot of caveats - to include that some battery management systems only balance the charge between cells after the battery is charged to 100%.

Thanks for the reference! He also said that charging to 100% can be more damaging than even a complete discharge. So maybe charge to 90% most of the time, but go to 100% periodically? I guess it's pretty silly trying to come up with a reasonable charging regimen without knowing what the BMS is actually doing.

 

[Deleted member 803]

Nonsense, drain your batteries at will and charge till the charger says fully charged. I've been doing this for years with cell phones and even leave my Note phone charging overnight. I have never had a problem with deficiency save the normal degradation that occurs over time with many cycles. My guess is that any name brand bike with a lithium ion battery and a charger will have failsafe system built into the controller and charger that prevents premature damage to the battery. I have talked to the folks who make lithium ion batteries in Japan (Samsung and Panasonic) and neither of them brought up any charging/decharging issues or restrictions.

 

[JoePah]

@BafangFan do you really think a $600 charger is necessary? If you really want to lower the charging voltage, and you feel a little confident handling electrical parts, you can remove your charger housing. Locate the potentiometer .. with the charger on measure output voltage. Then adjust the pot screw until the output voltage is reduced by 1 volt (or more if you want to charge it less).

Note" Before you make any adjustment, match mark the screw postion to a reference point, then take a picture.. This way you can restore factory setting if you want.

 

[Ebike Commuter]

The following link has some information related to the effect of charge voltage on lithium battery cycle life.

http://www.powerstream.com/lithium-ion-charge-voltage.htm

The information in the link provides data and charge profiles from a small lithium battery. Also, an equation that describes the effect of charge voltage on battery cycle life is provided. The equation suggests a strong effect of decreased battery cycle life with increased charge voltage.

There is some lack of clarity in the article. For example, how battery cycle life is defined is not mentioned. It seems it must be a decreased capacity below some fixed amount. Also, no reference is provided for the equation and it is not clear whether the effect relates directly to the charge event or the cumulative time at a given charge. However, if the information were applicable to larger lithium batteries, it would seem to predict that a lithium battery would withstand ~8X more charge/discharge cycles when charged to ~63% compared to fully charged.

Table from article shown below:

 

[Ravi Kempaiah]

The following link has some information related to the effect of charge voltage on lithium battery cycle life.

http://www.powerstream.com/lithium-ion-charge-voltage.htm

The information in the link provides data and charge profiles from a small lithium battery. Also, an equation that describes the effect of charge voltage on battery cycle life is provided. The equation suggests a strong effect of decreased battery cycle life with increased charge voltage.

There is some lack of clarity in the article. For example, how battery cycle life is defined is not mentioned. It seems it must be a decreased capacity below some fixed amount. Also, no reference is provided for the equation and it is not clear whether the effect relates directly to the charge event or the cumulative time at a given charge. However, if the information were applicable to larger lithium batteries, it would seem to predict that a lithium battery would withstand ~8X more charge/discharge cycles when charged to ~63% compared to fully charged.

Table from article shown below:
View attachment 4478

That is true. It's the only way Prius can guarantee 8 yr warranty.
If you go to Chevy Volt forum, you'll see lot more details about the SOC and battery life information. The battery on Chevy Volt is rated at 16.5 to 17Kwhr but usable capacity is only 10.5Kwhr (approx 61%) and owners who have driven the car over 200k+ miles report that they still get 40+ miles per charge.
So, the bottom line is get a ginormous battery ....

 

[JoePah]

Good chart. The better ebike suppliers like Cellman EMV3 supplies battery chargers that are user adjustable for charge voltage. The chart shows that even a 90% charge doubles battery cycle life. Not a huge range penalty