Li-Ion Battery Charging

The higher the IR (internal resistance) the lower the c-Rating. The lower the IR the faster you can discharge the battery.

If the IR is different on the hole pack the whole pack can get out of Balance.

it is fact that charging to 42 Volt is not healthy because you gain a Little bit extra capacity 20% but 40% less life span compared to 41V. (The numbers could be wrong but i think youll get me). Leaving the pack at 42v means charging --> reached 42V --> released and got to 40.9 --> charged again. (because it holds 42v just for a couple minutes)

That way the IR will raise faster. Am i wrong?


When I know stuff about stuff I rarely end my sentence with an interrogation point. Asking questions is usually a good way to learn stuff you recently heard about when you’re not sure if you should take what you read at face value and if it’s worth it to immediately change your ways.

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A battery that stays at higher charge state suffers faster degradation, that means that with time, even without discharging the internal resistance will go up

There is a reason most electric vehicles manufacturers make the available energy less than what the battery has or recommend the user to not use full charge daily


Everyone in what industry, I’m curious?

Laptops, cordless tools and etc you can look at all Battery Management system IC which are commonly used in devices with Li-Ion batteries :wink: All of them charge to 4.2V/cell and does balance to 4.2V


So your battery lives longers.


This!!! Especially in cold weather :slight_smile:

Correct. Older batteries have higher internal resistance. As you cycle batteries and use them over time the IR rises. This is important because, voltage sags proportionally with internal resistance, double the IR, double the voltage sag at a specified current. IR changes not only over the cycle lifetime of a cell but also during a single discharge cycle, I forget what the curve looks like exactly but IR is high at high voltage and at low voltage. It is way more pronounced in LiPos than Li-ions. If you look at a constant current discharge graph the voltage drops rapidly in the first bit and then steadies itself out and then drops rapidly in the last bit. This is due to IR changes. Also why your battery gets warmer towards the end of charging/discharging.

Over time, IR rises and you hit your low voltage cutoff sooner and sooner. When this time is equivalent to 75-80% of the the time the cell has as new, then they call it dead. Manufacturers try to put this in the 200-300 cycle range. As an example, 30Q cells can discharge at 22A continuously without any cooling. But their cycle life is only 200ish cycles, by limiting the current to 15A, they were able to increase this to 300ish cycles.

Here’s the relevant pages from their spec sheet:

I hope this helps with your understanding.

Sometimes you should listen to your own advice…


That’s all uses where use time matter more than cycle life and battery’s are “cheap” to replace

This, lower at almost full charge, little bit higher at full charge and way higher when empty

That’s why you don’t wan’t to discharge to 0% if you wan’t to have the maximum cycle life, for the same current, you have a lot more heat going into the cell at low state of charge, and more heat = faster degradation

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Thanks!!! I remembered it had a u shape (somewhat lol) :smiley:

Do you know what chemistry that curve is for? I remembered it being a lot more symmetrical for some reason. I’ve always done my IR checks at 50% charge thinking it was the best case scenario.

LoL, nice when you take stuff out of context :wink: My comment was that he talked that charger keeps 4.2V all the time it’s connected then it’s not true :slight_smile: and later tried to talk it out about IR.

P.S. If all your theories and scientific BS are so good why nobody uses it? Show me any of stuff implemented in like consumer level :slight_smile: All those talks about charging until specific voltages and etc and still, you use same plain old BMS chargers which act like everything else so at the end of the day it doesn’t matter.


If a charger keeps the battery at 4.2V, the IR will rise faster over time (and degrade faster) than if it was at storage.

Have you seen a Tesla Electric Vehicle?

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Is it consumer level? Nope its automative which is completely different eco system and standards :slight_smile: Plus Tesla runs computer level BMS where you can do whatever you want :slight_smile:

Maybe you should raise your standards then…


I don’t , just took one to Ilustrate, but i saw somewhere in a 18650 review

Try to buy some automotive parts in like Digikey :wink: That stuff most of the time requires NDA agreements and etc :slight_smile: But my point was science stuff always has some magic pills and engineering department just get shit done.

To a certain point I agree with you, a battery for our boards isn’t that expensive you can’t afford to replace when it is not performing as good as you wan’t

But if you can make something last way more by just following some simple steps, why not? less money wasted, less cells having to be recycled, less pollution from shipping, etc etc

The effect is small? Yes, for one person, if everybody do that kind of thinking in everything they do every day is lot

But for battery’s and extending cycle life:

  • Charge only what you need:

    My board can do 40km, but my round trip commute is 9km, I charge it to 39V, still have plenty of power and range, and my battery’s will last way more

  • If full charge is needed, make it be ready when you are about to leave:

    The less time the battery pass at full charge the better, less time to the electrolyte decompose and lower the battery performance and life

    The exception would be if you charge to a lower voltage, then you can put it to charge at night and not worry about

  • Wait for it to cool before charging:

    Same thinking, the aging process happens way more quicker at higher temperatures, by pumping current at it while at it’s peak temperature you are just making it happen faster


I bought to 10s liion charger. One Was a more expensive one from miamiaboards (41,5v) and one cheap Chinese one (40,5v)

Why is it common to not overshoot? Maybe there is a reason or i had luck. I am sorry that i dont have enough data for an empiric rule Evaluation…

I understand your points, and I believe they are good but how many people afford to check what level is battery at then charging most of them just plug them in and lets it finish charging. I will try to experiment with this sutff as I am designing my whole management system from scratch because good stuff is not available for consumers.

For e.g. how many of those BMS used her calculates coulomb in/out of battery, P groups each cell voltage (It’s really hard to spot dead cell in 5P groups as other cells in group just hide that cell low voltage) there is many key points from science you can do for battery to make it last longer but how convenient are they?

P.S. Thanks for reminding to charge my board :smiley:


Did you measured or just was written on it? If so measure whats happening for real :slight_smile:

Yeah, but a simple charger with adjustable end of charge and habit make it happen

On the BMS department we really need something adjustable, Battman was suposed to be that, now looking forward to @SimosMCmuffin BMS, the more options we have the better

P.S. Your welcome


Even if your charger measure 42V on the output your battery will never get to that. The vast majority of charger terminate after the current drops to a certain level, usually C/10, if you charge at 5A, it will stop charging at 0.5A, and since all battery’s have and internal resistance the end of charge voltage will always be lower