Is it better for battery life to charge at a lower amperage?

[Alaskan]

Bosch offers both a 2.2 amp charger and a 4 amp charger for their ebike systems. Intuitively it seems that charging at a lower (gentler?) rate could possibly be helpful in getting more charge cycles out of a battery. I have no evidence and have not read anything to support this hypothesis.

Does anyone with a greater knowledge or more experience with lithium batteries know anything that either confirms or dashes this idea?

 

[AguassissiM]

@Alaskan
The best person to answer that would be Battery Mooch, here is his YouTube channel .

 

[Ravi Kempaiah]

Bosch offers both a 2.2 amp charger and a 4 amp charger for their ebike systems. Intuitively it seems that charging at a lower (gentler?) rate could possibly be helpful in getting more charge cycles out of a battery. I have no evidence and have not read anything to support this hypothesis.

Does anyone with a greater knowledge or more experience with lithium batteries know anything that either confirms or dashes this idea?

As someone who is conducting research on batteries (yes, my PhD thesis is on batteries) AND owning/riding an E-bike (Bosch powered), I can share few things.

In theory it is good to charge at slow rates. Especially for cars. Tesla recommends not to use the supercharger quite often because it charges at something like 450A (compared to 4A or 2A E-bike chargers). So, they have very sophisticated BMS and power electronics to handle that level of current.

Bosch powerpack 500 uses cells in 10-4P configuration (e.g., samsung let's say 35E or Sanyo GA at 3350mAh).

4 cells in parallel * ~3.35Ah/cell = 13.4Ah
10 cells in series * 3.6V/cell = 36 volts.

36V * ~13.4Ah = 483Whr (rounded off to 500 Whr powerpack)

Now, 4 amp charger charges the battery from empty to full in (13.4/4 = 3.35 hours). The initial 80% happens in constant current mode. That means all the Lithium ions are shuttled back to the anode from cathode. Then, the charger switches to constant voltage mode and slowly tops it up to 100%. This accounts to roughly 0.28C or 0.3C charging rate. This is well below the standard charging rate for each cell (0.5 to 0.6C) for most high-quality cells)

Now, 2 amp charger charges the 500Whr powerpack in roughly 7 hours. This accounts to 0.15C. If you ran your bike on full turbo, you could literally drain the whole 500whr powerpack in 1 hour AND that is not good! That means you discharged it at 1C. That is why in Bosch dual battery configuration, it switches from one to another to avoid draining a single battery at 1C. By toggling between two batteries, even if you run the bike full turbo, it won't cross 0.5C.

Charging or discharging at 0.15C or 0.3C , both cases are well below the 0.5C standard charge rate. Slow charging does help but what really matters are these two points:

1. Keeping your batteries charged to 100% at all times is bad! (really affects the chemistry). That's why most cars use 20%-80% rule.
2. Exposing your batteries to high temperature during storage or normal E-bike usage.

In summary, slow charging is good but doesn't make a huge difference. The best case scenario is get a 1000Whr battery and only use 70% of it.

I have been charging my Haibike at 4A for 1+ year and the battery still holds great amount of charge because I don't fully charge it everyday and try not to expose it to high temperatures.

Hope this helps.

PS: I don't mean to come across as someone who knows it all. But, I spend a LOT of time researching these stuff.
If you guys find any mistake, feel free to correct me.

 

[Alaskan]

Ravi,

Please do not apologize.

Your information is just what I was looking for...the thoughts of someone who really knows something (as opposed to "has heard something") about the subject at hand.

Thanks for taking the time to shed some light on my question.

 

[Alaskan]

My bike came with the 4 amp charger. I purchased a 2.2amp charger, mostly for travel purposes as it is smaller and lighter. I guess I will just use it for that and charge with the 4 amp one.

 

[christob]

Hi @Ravi Kempaiah ... I'm confused by the way you wrote your 2 points near the end... I think you are saying that keeping the battery 100% charged whenver possible, is something to avoid doing? The first time I read it, I thought that you meant you DO try to keep it full charged all the time... but later you say that you don't do that...
Also... what counts as extreme/high temperature in your definition? Thanks!

 

[Ravi Kempaiah]

Hi @Ravi Kempaiah ... I'm confused by the way you wrote your 2 points near the end... I think you are saying that keeping the battery 100% charged whenver possible, is something to avoid doing? The first time I read it, I thought that you meant you DO try to keep it full charged all the time... but later you say that you don't do that...
Also... what counts as extreme/high temperature in your definition? Thanks!

Sorry, edited the post.

What really affects the battery chemistry is keeping them at high voltages. So, Yes, charge the battery to 100% but avoid storing at that point for extended time.

From my time on Tesla forums, I know that lot of Tesla owners set the timer so the car is ready with full charge just before they leave.
Imagine this.. you stretch a rubber band to its fullest length and then hold it for 1 hours. This will lessen the viscoelastic properties of the rubber. Similarly, if you keep the battery at 100% for a long time... the cathode and anode parts of the battery undergo lot more unwanted reactions and this leads to capacity fade.
That is why it is advised to store the batteries at 50% or less if you are not using for for couple of months.

This has been proven in 100's of scientific papers. I will be happy to link it if you are interested.
Normally when I charge, I stop it when it reaches the 80-85% mark. When I do need more range, I do charge it 100% but then I won't keep it for days like that.

Actually, storing the Li-ion batteries at cold temperatures is fine. I know in many scientific labs, they keep some cells at frozen temperatures and bring it back to the room temperature before using them.

The liquid electrolyte which conducts Li-ions within the battery gets solidified at very low temperatures (just like water or any other liquid) and resists the motion of Li-ions. That is why in winter, our E-bikes have lesser range. But, they come back up in the spring/summer.

Charging at super low temperatures is not good because we are pushing the ions through this thick cloud of electrolytes with brute force.

Most importantly, exposing the battery to high temperatures is really bad. You know Nissan had a multi-million $$ lawsuit against them because their Nissan leaf batteries died prematurely in Arizona. Check this out: https://insideevs.com/nissan-leaf-battery-settlement-get-final-approval/

If you combine high voltage and high temperature, then it's even worse. The safe temperature for Li-ion is 50'F to 80F.... I can safely say that above 100'F it's def not good for the cells.

Most E-bike battery temperatures don't exceed 100'F unless one is using the throttle all the way or using high level of assist.

In summary, time spent at high voltage or high temperature is bad.

Just to add some credibility to the discussion. I am linking to the exact point in a video where it is discussed.

Prof. Dahn is world's most eminent battery scientist.

 

[christob]

Thanks @Ravi Kempaiah for clarifying...
I currently don't have a charger that shows %... is there a third party device that reliably shows battery charge level? Nor do I have anything to tell me the battery's operating temperature...
Also... if 80-90f is a target "limit" for ideal battery health, do you simply stop using your ebike in summer, when ambient temperature outside could be say, 85-100?

 

[Ravi Kempaiah]

Thanks @Ravi Kempaiah for clarifying...
I currently don't have a charger that shows %... is there a third party device that reliably shows battery charge level? Nor do I have anything to tell me the battery's operating temperature...
Also... if 80-90f is a target "limit" for ideal battery health, do you simply stop using your ebike in summer, when ambient temperature outside could be say, 85-100?

I really don't think it's necessary to baby the battery to that extent. I don't like to micro-manage the battery %. An approximate guess is fine. What bike are you using currently?


The engineers have designed such that it provides enough power for normal usage.
Even in the summer, it works fine. I try not to leave the battery out in the sun for long periods but other than that it should work well. When you're biking in the summer, the ambient air flow should still keep the temperature down.

Most quality batteries bosch, Yamaha, stromer are designed to withstand some self - heating.

So, I wouldn't worry too much. It takes the fun part away. Just few simple things I take care of and I'm sure my batteries will last 3 years or 12,000+ miles with good enough range.

 

[surfstar]

Great info, as I have a 4A charger with my ST1. I aim to charge to 80% by guesstimating time on the charger vs % battery level shown on my LCD (roughly 1hr charging is 25% +/- for my pack size). Since my battery capacity far exceeds my commute, I can easily extend the battery life with this routine.

I guess, the other related question is, does the pack need a 100% charge to 'balance' the cells? If so, how often? Or is this dependent upon the specific manufacturer/BMS setup?

 

[Acey]

christob, here is what you need. These guys innovate a lot of equipment for e-bikes: http://www.ebikes.ca/product-info/cycle-satiator.html They sell on their Amazon shop, but often sold out. Hard to get, but worth the effort.

 

[Ravi Kempaiah]

+1 On the ´charge before you leave’. Good tip, especially if you need the 100% tank (often my case). I fill to 80% the night before, then topup the remaining 20%. But you have to be careful because the last 20% topup often takes longer than you expect.

That is because in the last 20%, the charging mode switches to constant voltage. Intuitively, what it means is imagine you were driving a huge train. Can you stop the train just like that? No. It takes couple of miles to bring the momentum down.
Similarly, while charging, millions of lithium ions were rushing to the anode and you can't stop that train just like that.
Slowly, you drop the current while holding the voltage steady.
So that is why good quality chargers take forever to get the last 20% done.

 

[Ravi Kempaiah]

Great info, as I have a 4A charger with my ST1. I aim to charge to 80% by guesstimating time on the charger vs % battery level shown on my LCD (roughly 1hr charging is 25% +/- for my pack size). Since my battery capacity far exceeds my commute, I can easily extend the battery life with this routine.

I guess, the other related question is, does the pack need a 100% charge to 'balance' the cells? If so, how often? Or is this dependent upon the specific manufacturer/BMS setup?

It depends on how smart the BMS is. There is absolutely nothing wrong with charging your battery to 100% once a month or few weeks. I do charge it full once 2-3 weeks and I do need the extra range.

 

[Johnny]

Great information by Ravi. It should be made sticky.

 

[Moonglow]

Hi Ravi, thanks heaps for this info. An old post but still feels pretty contemporary. Some of its sort of more known now than perhaps it was then, but still nice to have it so clear. It helps to feel a bit more confident and informed on what we can do to look after our batter, or where to relax a bit more! Like you say, while we've made a big investment in our batteries the point is still to have fun.

I have our charger on timer for about 6 hours from when I plug it in (turn off at 1am), but it sounds like for an automation like this it makes more sense to start the charger later and have it ready or as close to ready in the morning. This will be a bit easier with our new bike as it has a dual 500wh battery vs our current battery that's 3 years old, 20k km under it and starting to need a full charge to do our daily commute.

I did wonder about what your advice means for the Bosch dual battery charging schedule. It sounds like now they charge one battery to nearly full before starting on the other battery. So one is always getting a greater load.

PS, I imagine by now you're close to completing your PhD, hope its gone well. Any lessons for ebikes from it?

 

[Ravi Kempaiah]

Hi Ravi, thanks heaps for this info. An old post but still feels pretty contemporary. Some of its sort of more known now than perhaps it was then, but still nice to have it so clear. It helps to feel a bit more confident and informed on what we can do to look after our batter, or where to relax a bit more! Like you say, while we've made a big investment in our batteries the point is still to have fun.

I have our charger on timer for about 6 hours from when I plug it in (turn off at 1am), but it sounds like for an automation like this it makes more sense to start the charger later and have it ready or as close to ready in the morning. This will be a bit easier with our new bike as it has a dual 500wh battery vs our current battery that's 3 years old, 20k km under it and starting to need a full charge to do our daily commute.

I did wonder about what your advice means for the Bosch dual battery charging schedule. It sounds like now they charge one battery to nearly full before starting on the other battery. So one is always getting a greater load.

PS, I imagine by now you're close to completing your PhD, hope its gone well. Any lessons for ebikes from it?

Thanks for your kind words.
Yes, I defended my Ph.D. thesis earlier this year and moved to Canada to work with Dr. Dahn (the scientists in the video I linked above in this thread) and start an E-bike company (where Dr. Dahn is also an advisor and investor). We are currently designing packs that would last 50,000 kms or more.

I do have a dual battery Bosch E-bike and you're right. It charges one to 90% and then switches to another. Finally, they both go into CV mode where they are topped off.
As you suggested, it would be better to initiate the charging so it is ready just before you ride. This should provide several thousands of worry-free riding.
This thread may also be of interest to you: https://electricbikereview.com/forums/threads/e-bike-battery-guide.24443/

Cheers

 

[Moonglow]

Nice, congratulations, exciting milestone, amazing opportunity to come out of it and wickedly interesting project to be working on! Thanks for the link.