Best Charging Strategy for Li-Ion Battery?

[Markus Hanke]

I’ve a question that has been on my mind for a while, and I’d like to hear the opinions of people who are better versed in electrical engineering than I am. This is really not my area of expertise (nor interest, tbh).

So I recently acquired a digital device that is powered by a Li-Ion battery. My question is - what is the scientific consensus as to which charging strategy will maximise the lifespan of the battery? Assume room temperature as well as European climate humidity levels. Also assume common sense precautions, such as not leaving it plugged in unnecessarily etc.

I have tried to research this in the literature, but what I found is contradictory information - some authors argue that it is best to charge to 100% and then let it empty itself completely before recharging; others argue that it is best to keep the battery levels between 20%-90% roughly (actual figures vary). Yet others seem to say that keeping it in and around 50% by constant “micro-charging” throughout the day is best. They all give reasons, arguments and statistics that seem reasonable.

Is there an actual consensus on this? Personally I would think that avoiding extremes of 100% and 0% charge seems prudent, but I don’t know.

[StringJunky]

Hi Markus. The Battery University site is the place to look.  Practical strategy. Try and keep your battery above 20% before recharging, so use no more than 80% of the battery if possible.  Topping up everyday is much kinder than fully discharging until the device switches off. Never leave your battery empty for significant amounts of time....like  days. The battery's safe voltage range is 3.2v  to 4.2v. A lot of devices will switch off by default at around 3.2v. This saves some residual charge to keep the battery in safe condition. The 'ideal' range is to keep it between 20-90% charged. Most devices don't actually charge to 100%... overcharging is problematic from a safety point of view, If you use the device everyday, charge at the end of the day or after use.  Regular discharging to exhaustion really shortens the battery life. Bear in mind practical realities will dictate that you will run it it down now and again to off... you can't avoid it. I get about 2-3 years of everyday use before I think the maximum charge capacity has fallen by half. If battery life matters, don't use quick charging and don't use the device straight after charging, if possible. These are things to aim for but life dictates otherwise sometimes. Avoiding excessive discharge and heat are the main things. To summarize: daily charging is much better for battery life and safety than running flat then charging. Long term device storage when not in use wants to be around 50% filled.

Edited December 8, 2020 by StringJunky

[Ghideon]

1 hour ago, Markus Hanke said:

They all give reasons, arguments and statistics that seem reasonable.

Good and well formulated question. I have no concrete answer to provide but I may offer some experiences regarding the numerous different reasons and results. As far as I know the strategy built into the charger or device have an impact. I have had devices with no monitoring of the charging, the charging continued until manually disconnecting. The batteries did not last long, I neglected the issues of overcharging etc. I also have devices where the charging strategy is built into the system; temperature, voltage etc is monitored in attempt to optimize the charging. It also tries* to track my personal usage of the device in an attempt to extend the battery life by optimizing the charging strategy. This means that for the same type of battery I would have a very different opinion on a suitable strategy depending on which device I had in mind. And also very different statistics if I had been measuring the outcome.

 

*) I have no data on how successful this approach is, I have no data.

[StringJunky]

1 hour ago, Ghideon said:

Good and well formulated question. I have no concrete answer to provide but I may offer some experiences regarding the numerous different reasons and results. As far as I know the strategy built into the charger or device have an impact. I have had devices with no monitoring of the charging, the charging continued until manually disconnecting. The batteries did not last long, I neglected the issues of overcharging etc. I also have devices where the charging strategy is built into the system; temperature, voltage etc is monitored in attempt to optimize the charging. It also tries* to track my personal usage of the device in an attempt to extend the battery life by optimizing the charging strategy. This means that for the same type of battery I would have a very different opinion on a suitable strategy depending on which device I had in mind. And also very different statistics if I had been measuring the outcome.

 

*) I have no data on how successful this approach is, I have no data.

Such devices should not be used if they do not have undercharge and overcharge protection.

https://www.cassindustries.com/lithium-battery-charge-cutoff-testing/

[studiot]

4 hours ago, Markus Hanke said:

1 have tried to research this in the literature, but what I found is contradictory information

2 hours ago, Ghideon said:

Good and well formulated question.

 

I agree.

I also agree that the battery university is a reliable site.

 

Markus you also need to know that charging techniques are different for different types of battery.
So I'm glad you mentioned Lithium-Ion.
The practice of taking discharging the battery pretty fully before recharge and even taking it down to deep discharge occasionally applies to old fashioned accumulators- lead acid batteries and also to NiCads.

More recent Nickel - metal hydride batteries can be safely recharged at any state of charge without detriment and can also sustain quite high rates of recharge, such as would destroy the Nicads that preceded them.

More modern are the lithium ion technologies which are implemented in several ways.

In particular the low current drain 'polymer' batteries are very sensitive to abuse as the charge is spread out over a large area on a very thin film.
This can easily be punctured by heat or excessively fast or just excessive charging or discharging.
For your digital device these are most likely to be the types meant.

Power tool Li-ion batteries have a different 3D construction and are more robust so can be fast charged and supply high currents (fast discharge).

So use the correct charger or charge lead if USB powered and keep within String Junkie's limits.

 

[Markus Hanke]

@StringJunky, @studiot: Great, thank you so much for the responses  +1 for each of you!

It is as I myself would have expected from some very basic principles...I just wanted to be sure and hear from the experts, since I need that particular device to last for a while.

One more question though: the manufacturer actually states that the battery has an average expected lifetime of around 500 charge cycles. So when I, say, use 20% charge in a day, then recharge by the same amount of 20% in the evening, does this count as a full “charge cycle”? Or is a charge cycle defined as the accumulated (not necessarily in one go) charging and draining of the battery’s total capacity?

This may be a stupid question, but like I said, this isn’t my area of expertise at all.

[studiot]

2 hours ago, Markus Hanke said:

@StringJunky, @studiot: Great, thank you so much for the responses  +1 for each of you!

It is as I myself would have expected from some very basic principles...I just wanted to be sure and hear from the experts, since I need that particular device to last for a while.

One more question though: the manufacturer actually states that the battery has an average expected lifetime of around 500 charge cycles. So when I, say, use 20% charge in a day, then recharge by the same amount of 20% in the evening, does this count as a full “charge cycle”? Or is a charge cycle defined as the accumulated (not necessarily in one go) charging and draining of the battery’s total capacity?

This may be a stupid question, but like I said, this isn’t my area of expertise at all.

thnx.

Most devices these days have some sort of charge status indicator.
The 500 charge/discharge rating refers to charging until that indicator says full and the recharging until that indicator says recharge.
Note el cheapo replacement batteries usually have a lower life expectancy  -  around 350 cycles is common.

Again String Junkie's advice is spot on think of your average cellphone.

A simple phone will require recharging every 3 days to a week so the batery will last several years.
A heavily used smartphone may run out before the end of the day  many find this because they have too many apps or the machine keeps activating with wifi data roaming switched on.
Such a battery may not last much beyond one year. Since some folks change their phone like I change my socks, they never see this problem. (Does the Zen Master rigout include socks ? I can't tell from the avatar).
I always try to get a spare battery and a charger (these are available for most devices) at or near purchase.

 

 

[md65536]

A lot of the cautious best practices depend on whether you're talking about a battery pack or a single cell. I'm not sure if charging a single cell to 4.2 v will have a noticeable effect, but if you charge a 2-cell series pack to 8.4 v, and they're not perfectly balanced, you might eg. charge one to 4.15 v and the other to 4.25 v, more likely shortening its life. Avoiding charging to full might make a pack last longer, but do nothing for charging a single cell?

Letting a cell drop below 3 v once might shorten its life a little, but driving it negative in a very unbalanced battery pack will quickly cause damage.

Charging with lower current is better. "Rapid charging" devices likely have shortened life span. It's also something to be aware of with replacement batteries, because a charger made for a 2400 mAh cell might stress a 2000 mAh cell. Charging at an excessively low current would be the easiest on a cell.

Edited December 9, 2020 by md65536