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Battery Basics for Beginners [Serious-ish]

I see the same question being asked by many newcomers here so I would like to shed some VERY BASIC info on batteries used in esk8, notation, configuration, ratings, etc.

Battery Notation

Common battery notation you keep seeing or will see is a (XX)s(YY)p battery with (ZZ) cells:

  • XX is the number of batteries you have in series ( s ) type connection.

  • YY is the number of batteries you have in parallel ( p ) type connection.

  • ZZ is the actual battery cell type used. Samsung 30q is by far the most common here. You will also see 18650 mentioned a lot. That is just the physical dimension of the battery cell, nothing to do with chemistry. It’s a battery 18mm wide by 65.0 mm long. Panasonic, Sony, LG, etc all make 18650 cells. Samsung makes them the best per price for our application. They also make other size cells like the 20700. Can you guess what size that is?

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Battery Configuration

Series

When you add batteries in series, it adds to the total voltage available to your system.

ex. 30Q cells are 4.2V fully charged,

Ie. 10s is 42V, 12s is 50.4V, 100s is 420V etc.

Parallel

When you add them in parallel, it keeps the voltage the same but adds to the capacity (measured in Ah or more commony mAh).

30Q cells are 3 Ah each (or 3000 mAh if you prefer).

Ie. 4p is 12 Ah (12000 mAh), 10p is 30 Ah, etc.

Very very basically, increasing series adds speed, increasing parallel adds range.

Lipos

Lipos are safe if you maintain them well. If not, they can puff and make fires. A lithium ion battery pack like discussed above can still burst into flames if you wire it wrong or don’t protect it but are generally safer and easier for beginners. They can give slightly more voltage (power) but also sag faster.

Battery Cell Ratings

Yes, voltage and capacity (those mAh numbers) matter very much. Remember the examples above with series vs parallel?

25r cells are 2500 mAh cells and sag faster than 30q
30q cells are 3000 mAh cells - comparative example
40t cells are 4000 mAh cells and sags less than 30q

25r is what many prebuilts use and are fine. They just won’t carry you very long. Most newcomers I see are upgrading their prebuilt batteries with 30q packs.

You can not mix cell types. Also don’t mix cells of different age (how many times they’ve been used/charged - called cycles).

After the Battery Upgrade

Your motors are dumb devices. They will happily take whatever your battery sends at them even if it melts them into oblivion. This is where your electronic speed controller (ESC) comes in. It sets the limits of amps (and tons of other things) going to your motors using complex maths I won’t get into. As long as your ESC can handle the voltage rating of your new battery, you’re good to go. You will find this in the esc specs.

BMS and Charging

It stands for battery management system (BMS). It is wired to your battery and keeps the charge even across all of your parallel groups so your battery doesn’t get unbalanced and have problems.

You can charge your pack at different rates as long as they match your pack’s voltage. The charger will be rated in amps to let you know how quickly it will charge your pack. Might as well charge as quickly as possible right? Eh not so much. Charging too quickly is bad for cells and will shorten their lifespan. Charging slowly is best for your pack but worst for riding your esk8 around aot.

Here is a conservative charge rate formula that isn’t painfully slow either:

[# of parallel groups] * [cell type mAh rating / 3000]

For a 10s5p 30q pack (30q cells rated at 3000 mAh):

[5] * [3000/3000] = 5A charge rate.

Again, you can certainly charge faster or slower than that, this is just my personal recommendation.

Do not ever let your battery pack drain below recommended levels! For this reason, many bms and escs have a hard voltage cutoff where your board will cut all acceleration when too low (cutoff end). You see this happening most going up hills as this draws more power. Most escs used here take it a step further and implement a soft cutoff where, instead of throwing you on your face at a low voltage level, it will slow your board down gradually going to that point (cutoff start). Almost like you’re wounded and limping home to your charger. This brings up the next question, what is a safe discharged rating?

10S li-ion conservative (42.0V charge)
cutoff start 35V
cutoff end 32V

10S li-ion aggressive (42.0V charge)
cutoff start 34V
cutoff end 30V

10S li-ion max-range (42.0V charge)
cutoff start 36V
cutoff end 30V

12S LiFePO4 (43.8V charge)
cutoff start 34.5V
cutoff end 33V

credit to @b264 for saving me the typing


Please keep comments to basic-moderate battery related questions. All advanced battery construction questions should be posted in the battery builders club thread and ONLY AFTER READING THE WHOLE THREAD please.

Welcome to esk8!

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This needs to be the beginnings of an article for ESK8.news

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I’m open to revising and clarifying if anyone has suggestions.

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Deffo talk about cell charge and discharge rates

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I would disagree with this statement. I would say you should not mix cell types, unless you know exactly what you are doing and why. This is probably getting more into advanced territory, and you are (99.9% correct from a beginner perspective) but I’ll expound on what I know and correct me if I am wrong for some context on why you should not mix types and why someone would:

Put as simply as possible, IF you are mixing cell types, you shouldn’t be pulling more amps from each P group / # cells in each P group than any individual cell type is capable of handling, while taking into account ohms law and each cell types measured internal resistance. Internal resistance is huge when it comes to mixxing cell types, because cells with lower IR will tend to have more amps pulled from them (and may be more than they are capable of providing). The same # of different cell types should be the same across P groups (2x VTC6 + 6x 30Q for each P group- not 3x VTC6 for one group and 1x VTC6 the next). The only time I could see mixing cell types being useful would be for packs that mix high IR high capacity cells with low IR lower capacity cells for P group charging for range and high A output for power… even then it’s kind of dumb, lots of math would need to be done to ensure your pack is safe to pull the amps you need, and since cells vary wildly in specs and lifespan mixed cells would need to be chosen wisely for a pack that is reliable and safe long term. Also, different cells as they age the IR changes at different rates not only cell to cell but differently between types of cells.

So, again imo, cells should not be mixed unless you know exactly what you are doing beforehand and have done the math based off real world measurements to verify your math prior to loading your pack. In the context of new builders, sure it’s safe to say never just go mixing different cell types, ever. Feel free to disagree with me, I’ll hear you out.

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I fully agree and almost added a caveat about this but figured no beginner (target audience) should be assembling their own mismatched packs for safety reason.

Saying you can do it may lead noobs to thinking of it as an easy way to upgrade their board.

Your point is valid and taken. I appreciate your clarifying for readers.

@akhlut I agree. I will mention it here but I also want to expand more on that in a “how do I know what esc settings I should use?” as that is the most common esc related question I see here. I will pm a few of you gathering info.

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I’m here to help.

:smiley:

Collating this information is fairly important to new builders.

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Need to visit the topic of internal resistance. Its such a big part its hard to ignore.

(realised this was for beginners)
Maybe a small section after the basics for the extra lesson? Such as degregation, IR, dendrites, temperature dependencies, etc

and maybe most important of all; a source to stated information

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Good idea but as you mentioned, for beginners, I feel that would be better suited to a more advanced battery analysis and comparison thread.

Don’t want to scare away too many newcomers with a wall of charts and graphs. :slightly_smiling_face:

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Hopefully the DIY:er is familiar enough with what current, voltage and resistance is. But maybe thats too much to ask? :exploding_head:
Maybe a disclaimer is in place; do not play with shit if you dont understand it yet? :rofl:
Small sections of information is enough I think, graphs get boring quick :slight_smile:

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This might be a whole can of worms but maybe a small section or note to state what voltage is considered fully discharged.

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Seems like a basic enough point to make. I’ll add it, thanks!

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Would appreciate a section on calculating total continuous/peak discharge from P groups & cell specs, and how that impacts how you set your max battery amps on your ESC. Good write up!

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For series/parallel, both adds range, as to why they both do, probably don’t need to be mentioned in this basics guide.

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Constructive criticism: add a brief explanation of C

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Or just simplify it that total number of cells regardless of configuration determines the total watt hours, or the “size of your gas tank”. 10S5P with 50 cells has a very slightly higher capacity than 12S4P with 48 cells for example…

And if necessary expound upon it by saying it’s your total (nominal) voltage x total Ah per P group. Using the previous example:

  • 10S x 3.6v per cell nominal x 3Ah per cell x 5P per P group = 540 Watt hours
  • 12S x 3.6v x 3Ah x 4P = 518.4 Wh
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Is it just me or are C ratings totally backwards and unintuitive when you just want to know how many amps your battery can handle? This is a great suggestion.

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Agreed, Voltage and Ah are already in the text, might as well define Wh.

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Thanks for this writeup, Justin :smiley:

More information about cutoffs can be found over here

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This is kind of like soldering on cells. You should never do it. Those that do it, know exactly what they are doing and why, and what damage it can cause, and how to solder in a way that drastically minimizes that. But I would still recommend never doing it. Anyone who knows enough about it to do it, knows they can disregard that advice, because they know enough about it and what’s happening inside the cell.

Yes, this :arrow_up: So basically, never do it.

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