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New user looking for battery? Read this - COMPLETE WALKTHROUGH OF BATTERIES

battery
liion
lipo
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#1

So I was recently asked for a good link to a break down about batteries. Unfortunately, I didn’t have a good link to point him to, so I wrote my own. I decided to share it and build on top of it for the community. I will try to remove my opinions as much as possible, so sorry if I seem biased at times.

A FOR WARNING: Take all manufacturer ratings with a grain of salt. A guy on reddit named mooch315 has tested a lot of cells of all different formats, but especially 18650s, and you can find those test results here. His tests show some cells rated to 15a are actually higher discharge cells then some that are rated to 30a. Manufacturers do their own testing, so mooch315’s goal is to give the world an objective rating and view of the cells he tests.


Formulas you need to know:


mAh = 1000*Ah
Wh = Ah * max voltage
W = Amps now * voltage now

Lipo vs Li-ion


Li-ion is great for:

  • Flat ground riding
  • Riding slowly
  • Light riders

Unless you do a really large pack (6p or higher at 10s or 12s). They sag, which means the voltage drops quickly for a short period of time under heavy discharge, to go back up to slightly less than where is was before the heavy discharge after the heavy discharge is over. If your using current control (as most are with the VESC), this means you lose power (since you have less watts, reference formula #3 above). They are incredibly safe. The tests they do which are listed in the spec sheet are incredibly abusive, yet none caused a fire or explosion. Likely most of those same tests on a lipo would cause a fire or explosion. Larger packs (10s7p or 12s6p or larger) can overcome the sagging issue, as does setting your amp limits lower. Most cells say you can discharge up to 20 amps continuous. However, you will lose quite a bit of range at that number, and you want to aim for more like 10 amps continuous per cell in parallel.

Lipos give better performance if using a smaller pack, but they can’t take abuse well (discharging too low or over charging too high), and can become volatile. The discharge curve is different. Li-ion drop off a lot at the beginning, and then discharge at a steady decline. Lipos drop off a lot at the beginning, and then slowly decrease in voltage, and around 3/4ths of the way through the discharge, they drop off a cliff. The result is lipos give a better performance in current control mode than li-ion batteries of the same size (i.e voltage and Ah).

There is a newer firmware mod which was created by @Ackmaniac that allows for watt control mode, which should get ride of this problem. But that’s another whole discussion in it’s own.

Here’s the is discharge curves of an average lipo and li-ion cell. Look at how quickly the line going from right to left goes down.

NOTE: Not all lipos or li-ion cells discharge exactly like this. This is a generality.

Lipo Discharge Curve:

Li-ion Discharge Curve

Li-ion cells come in a few varieties. The most common is the 18650. The 18 refers to the diameter of the cell in mm, and the 65 refers to the length of the cell in mm. There’s also the 26650. The most common 26650 cell is the A123 cell.

Lipo cells come in all manners of shapes an sizes, expect cylindrical cells (funny enough). They can be very flat, or very thick, in any of the x, y or z directions. Instead of a storing energy in this cylindrical shell, they energy in a pouch. This pouch is easy to puncture, unlike the li-ion cylindrical shell, which is one of their weaknesses. I don’t think I need to tell you want happens when you puncture a lipo battery.

Another thing. Lipos are rated to around 1/3rd of the life cycle of li-ion packs. So while lipos look cheaper up front, li-ion can be cheaper in the long run if you take good care of the cells. Obviously, the higher rate of discharge per cell in li-ion packs, the less life they will have. This is not a linear thing, so a 12s3p will not have half of the life cycle of a 12s6p. At 20a con, the cell only gets 400 full cycles. at 10a max, you get 1200 full cycles. so the 12s6p should in theory, if they are both ran at the same max amps, get 3 times the life, not double the life, of the 12s3p.

So to sum it up, heres the cost/benefit analysis.

Li-ion Pros

  • Safer (by a lot)
  • Longer life cycle

Lipo Pros

  • Sags less (thus when you draw high amps in current control mode, which most use with the VESC, you don’t lose power (and in this case, power refers to speed and/or acceleration))
  • Cheaper
  • Can be put into shapes not possible with a li-ion cell (great for boards that need to be thinner than 18mm)

I should mention now, that there is another technology called LiFePO4 or Lithium Iron. These give you the same shape as a lipo, same high discharge rates of a lipo, but are safer and have a longer life cycle than lipos. Seems like a win-win, but they are very expensive compared to both li-ion and lipo, and theres not a lot of sources out there for Lithium Iron batteries, so they are not very commonly used.


Parallel vs Series


Theres 2 configurations of cells. Parallel and series.

Parallel means negative to negative and positive to positive. The result is two cells become essentially one. They will automatically balance each other out to the same voltage. Parallel config doubles the Ah, meaning you’ll get more range.

Series means the voltage is doubled and the Ah stays the same. To do this config, hook one positive to one negative, and use the open positive on the one cell and open negative on the other cell to discharge.

Higher voltage means more power and less amps need to be drawn.
Higher Ah means longer range.

However, Wh or Watt Hours is the best measurement of the size of a battery.

Stay you have 12 li-ion cells. The typical li-ion cell is 2500 mAh in size, and is a 1s (since it’s 1 cell at a 3.7 nominal voltage).

You could do a a 12s1p (12 cells in series, 1 cell in parallel) or 1s12p (1 cell in series, 12 cells in parallel) or, since nobody would typically do either of those con figs (unless using the A123 cells, which are the cells boosted uses, in a 12s1p), a 6s2p would be usable, but still weak. The point though, is going between series and parallel, they all have the same Wh, since we have the same amount of electricity being stored in all of those configs.

Most people aim for a 10s or 12s, because you can get a lot of power and draw less amps. The more amps you draw from your battery, the hotter your battery and esc will get.

Many still use a 8s or 6s battery, but it’s more of a budget board thing. Boards at those voltages are weak when compared to the same board at 10s or 12s.

To get more range though, since you can’t really go higher than 12s (very few esc’s can handle higher than 12s), you put more cells in parallel to get more range.

Back to our example, a typical li-ion battery in:

12s1p will have 2.5 Ah total at 50.4 volts. 2.5 x 50.4 = 126 Wh
6s2p will have 5 Ah total at 25.2 volts. 5 x 25.2 = 126 Wh
1s12p will have 30 Ah total at 4.2 volts. 30 x 4.2 = 126 Wh

No matter the config, all of these batteries will have around the same range, since you have the same amount of cells (thus same amount of electricity) in all of these configs.

This is why when comparing peoples batteries sizes and ranges on here, we usually reference the Wh of our packs, not just the S and P of the pack.

IMPORTANT NOTE: The legal limit to fly on an airplane in the US with a battery is 99 Wh, so if that’s important to you, keep this in mind. Europe has similar rules also.


Sag


Sag is directly correlated between max amps you will draw to max amps you can draw. if you plan to draw no more than 60 amps, and have 240 amps, your result is little sag. If both of those numbers are 60, expect a large amount of sag, which means decreased performance and less range.

Sag is completely normal, in both lipo and li-ion cells. They will both sag, but to different degrees.


Charging Batteries


Li-ion cells are pretty easy to charge. You can use a standard “laptop” style charger at the max voltage of your battery pack (for example, a 12s battery needs a 50.4v charger, since 4.2 (max voltage per cell) x 12 (number of cells in series) = 50.4). Most Li-ion packs use a BMS or Battery Management System.

Lipo batteries however are usually charged using a balance charger. These chargers accomplish the same goal of balancing the cells during charging as the BMS, but without the need for a BMS. The downside is you need to plug balance cables into the balance charger, so charging now means more cables to deal with.

Both li-ion and lipos can be charged through balance chargers or laptop style chargers (with or without a BMS). You would not use a BMS and balance charger together however.

Most use balance chargers with lipos because a balance charger is cheaper and easier to use than a BMS, and lipos, according to manufacturer data, last about 1/3 of the life cycle of li-ions. Li-ion batteries are more expensive and last 3x times longer (again, theoretically), so a bit extra for the convince of the BMS makes sense. However, a BMS for a lipo is not a bad idea if you plan on replacing your lipos with the same lipos when they die, as you can use the BMS with the new battery pack, since it’s the same battery.


Battery Management Systems


Most li-ion batteries use BMS’s, but most lipo packs do not. The reason being lipos are usually charged using a balance charger, while li-ion’s use a “laptop” style charger. The “laptop” style charger simple provides a voltage at a constant amperage. The battery charger does exactly that too, but when a cell reaches 4.2 volts, it will start discharging is at the same rate through that cells balance lead, thus leaving that cell at 4.2 while the rest of them catch up. The BMS does exactly the same thing.

The goal of the BMS is simple: make sure the cells are all very close to the same voltage after a full charge, prevent cells from discharging too low, and prevent cells from being charged too high. Since the VESC can prevent cells from discharging too low, most just use the balancing and preventing cells from charging too high features of the BMS.

Again, as stated above, both a BMS and Balance charger accomplish the same goal with respect to charging. The BMS is more convenient though, as you need 1 cable instead of multiple to charge.

My opinion about flying with batteries


If you want hot swappable batteries that are under 99 Wh, Lipos are a better option IMO because 99 wh 18650 li-ion batteries will not output very many amps. This will result is horrible sagging and a bad experience (to me at least, cause I like a lot of power).

The Lipos I recommend are the Zippy Flight Max 8000 mAh series, either 2s, 3s or 6s linked in series. The 30c version at 12s and 8 Ah is capable of 240 amps continuous. The li-ion version of that would be basically a 12s3p, which is capable of 60 amps continuous. Remember, always take advertised numbers with a grain of salt also. Most of us will want 60 amps at least continuous. Though that 12s3p li-ion can do 60 amps continuous, it will sag very badly.


My Recomendations


If you do use lipos, get a good balance charger (not a knock off imax, cause those things are dangerous) and set it up so you can charge them quickly (if doing 4x3s, wire it so you can disconnect and charge them as 2x 6s’s, since most lipo chargers are limited to 6s, and they’ll charge faster this way). If you take care of them, lipos are safe. I’ve used over well over $1000 worth of lipos (which is quite a few battery packs) without any incidents, even when I have abused them. All lipo fires (besides when theres a known problem with a cell) start during charging or discharging, and almost always, it’s during charging. That’s why a good balance charger is important. They will almost certainly not explode if they are not charging or discharging, unless you puncture a cell or physically abuse the cell.

If you use li-ion, try to keep it to 10a max per cell in Parallel. This will reduce sag, increase battery life, and increase range. This can be tricky, which is why I recommend a 12s6p (the same pack that @chaka also recommends to eliminate sag) or higher in size. Smaller packs will work, but they will negatively impact performance.


Sourcing

The biggest problem for batteries is finding where to buy them.

Lipos are easy, I’d recommend HobbyKing first and foremost. They have a great battery finder that helps you find a battery that will fit to your specs.

Li-ion however, is hard. There are so many knockoffs out that that even telling the difference between a real and fake cell is almost impossible without testing the cells first for performance. I know some have recommended Battery Bro before. If others have some recommendations, please post below and I will update this. Amazon is hit or miss, and banggood from what I’ve seen is mostly miss.

For BMS’s, Best Tech Power and Su Power Battery are both commonly used sources.


Final Thoughts


I hope the world of batteries is a bit clearer to you now. Everything in this guide is what I have learned through first hand experience of building and testing electric skateboards for the past 2 years. If anything seems mis-leading or incorrect, as always, please let me know. My aim is to be as factual as possible, while giving new users a good insight into batteries.


How many batteries do i need?
Focbox vs VESC differences
Does mah matter when buying a lipo battery
How many batteries do i need?
The Kic Board V1.0 I Chinese Build
Building 10S3P Samsung 25R
WTB a board for under 300
First Build Log - Esk8Mint (working on that name)
[WIKI] A beginner guide to DIY an ESK8
[WIKI] A beginner guide to DIY an ESK8
Super Cell batteries
Lipo's vs Lion?
#2

another option lifepo4 or li-IRON which have about 4 times the cycle life of li-ion and you can literally cut a charged cell in half with a saw (done on endless-sphere), and it rebounds from over- charging or over discharging really well. They run at a slightly lower voltage and they aren’t quiet as energy dense so bigger and heavier and more expensive but looking at the cycle life it ends up being cheaper long run and piece of mind knowing no matter how stupid you act you can’t blow up your house


Noob question thread! 😀 ask your questions here!
#3

If you look carefully, I mentioned lifepo4 batteries. I just don’t seem them as practical for a new user, given the voltage differences, they are more difficult to source, and harder to find information about. This is for new users :stuck_out_tongue:


#4

Iron you can get in all types of shapes and have roughly 4x the cycle life of li-ion and are much safer and really not hard to find. I just convinced a new-to-this friend to get them as Iron being so safe they seem better suited for new people. They also sometimes have cool screw connectors such as headways cells where you don’t need to solder.
I should probably have gotten long ago and saved myself a bunch in ruined lipos.


#5

As far as I’ve seen, almost every lifepo4 on the market is sold from sketchy looking websites as off brand cells. Samsung, Panasonic, and LG are not making them. They are not a staple in the RC community either, so very select name brand RC companies are using them.

Once you get people using a different voltage system (not 2.8-4.2). I can see a lot of confusion. Getting help will be more difficult, and finding info will be more difficult.

These 2 reasons alone are enough for me to not encourage new users to use lifepo4.

Not to mention different BMS’s, chargers, ect. The general rule of thumb when your teaching someone is you use tried and tested materials and techniques. Since not a lot of people are using them at this point, I wouldn’t call them tried and tested, and the voltage difference adds another layer of complexity to it. Understanding the 2.8-4.2 voltage system along with this new voltage system, on top of everything else they need to learn, seems like a burden, that’s more likely to lead to problems than success.


#6

As somebody totally new to Lipos I have a few very simple questions that may be useful to other beginners if you decide to incorporate them into your guide (which is really well written and informative by the way, thanks) - What is best practice for brand-new, right out of the box lipo batteries? I thought I had read there is a typical “storage” capacity (3.7v???) so should you charge them first thing? I was planning on hooking up just 1 of my new 3s lipos immediately after my build just to test (like, does the motor move at all? Yes? Does it roll with me standing on it? Yes? - OK, I’ll plug them in and go for first ride after they charge…)
What are the nominal voltages? ie. a typical lipo can carry a max charge of x.x per cell, and should not be discharged lower than x.x per cell.
is it better/worse/no diff to balance charge 2x3s together or individually? Does it actually take twice as long to charge 2 3s batts one at a time as opposed to together?

Those are mostly the things I don’t know and was going to ask over the weekend (the last of my parts just arrived, it is first-build weekend for me!)

Thanks again!


#7

Lipos storage voltage is 3.7 volts. The best practice is leave them their untl your boards ready. Then to charge them when your ready to 4.2 volts, and discharge them all together as one pack most of the way down. This primes the cells in a sense.

Then either charge them to 2.7 again, or back up to 4.2 if you want to ride.

Do not every discharge the cells without the other ones. As cells deteriorate, they their capacity goes down. You want all cells to be at the same voltage during the entire discharge. Using one pack more than the rest will result in the cells that have been discharged more being in a different place during discharge in the future. This will lead to cells coming unbalanced more, and possibly, killing a pack all together because you’ll pull it too low while the other packs stay at a same voltage. Remember, the VESC can only save a battery a whole from going too low, not individual cells or packs. I’ve have wasted hundreds of dollars on cells by doing this multiple times before.

3.0 to 4.2, 3.7 is known as the nominal or storage voltage of a lipo. Remember than li-ions are different. li-ions range from 2.5 (I do 2.8 to leave some buffer room) to 4.2. (I know your dealing with lipos, but just a note for future users :P).

I would do 3.2 - 4.2 per cell cause lower than 3 and you shouldn’t bother trying to charge it anymore for safety reasons (resistance goes up, which while charging, causes pressure to build up inside the cells, they puff, and eventually, explode. If you want to know how big of explosion, you’d be surprised. Just youtube “zippy explosion” and you’ll see, lol).

If you really want them to last, do 3.2 - 4. Doing so means you cut off the top and bottom 15%, which should in theory, almost double the life of your battery pack. Theres also very little usable power in the top or bottom 15%, so your losing a few blocks of riding for a typical 8 Ah pack.

No difference in terms of the cells health or life cycle. If you have a 6s charger for example, but charge them as 3s’s, then your going to have to wait for one to charge, then charge the other. It’s quicker to charge them together at a higher amp rating. But if you charge a 2x 3s at say 2 amps, one after the other, or a 6s at 2 amps, you’ll wait the same amount of time. Amps are basically the unit that we use to describe power going in and out of the battery. Unless you charge the 6s at a higher amp rating, do them by them selfs will be no quicker.

What will speed things up though, is using a higher charging rate (Be careful not to set it too high. They say 2a or less is the best for the cells life cycle, even if it’s rated way higher) or if you have a charger that can charge four batteries at once, charge them all separately at 2a each and it’ll take have the time (since again, you’ve effectively double the rate on amps going into the battery).


#8

lifepo4 cell are far from new and untested. They are sold by many vendors more reliable than hobbyking.

you can easily adjust almost every charger’s voltage. Even li-ion and lipos have different voltage ranges and it’s not that complicated.

I recommended them to beginners so they wouldn’t need the complications of a bms as they’re surely safe enough to monitor on your own. I think that’s a huge simplification.

the only downsides are they’re more expensive and less energy per cycle but as far as simplicity, reliability, and safety, which are key ingredients for beginners, I recommend them first.


#9

3.5 lowest discharge and up to 3.15 for lipo is the more common range for preserving the cell. there’s almost nothing beyond 3.5.
discharging past 80% can result in extreme differences in voltage of different cells and that’s where unbalanced cells really show up and cut off the bms or plummet into death


#10

Does anyone have a data logged amp curve on a high voltage setup? I’m curious on how much amp is needed for the various tasks so I know how much amp i need to build the battery for. And how much can the vesc 4.12 or 6 handle of this amp. I see you Are takling about lipo with 200 amps plus but then I read about burning vescs above 50amp so where is the sweet spot?

My goal is a dual 6374 setup for hill climb and cruise. 90kg rider (95ish all up).


#11

Think of it like amps are the force that make you move. What will make you pull more amps?

  • Weight
  • Hills
  • High speed (wind resistance is a quadratic formula)
  • Punching the throttle
  • Motor Efficiency

I think your question is the most basic question that everyone wants to know when they first start. The problem, theres no one size fits all answer, because our setups (board, environment, us as people) are all different.

I for example weight ~200 lb. I will pull 80 continuous at times on certain hills, peaks over 100 amps.

Most of the time, I pull more like 50 amps continuous. Bear in mind, the motors I’m using likely could improve in efficiency, I’m a bigger guy, and I live In hilly San Francisco. So my environment is extreme to say the least.

Remember, that a VESC 4.12 can do 50 amp max, 27 amp continuous. I think for 95% of riders, a dual VESC 4.12 is enough. Between the 2 VESCs, 100 amps max and 54 amps continuous. However, theres no one size fits all here, so it’s something everyone will have to experiment with. In this tough environment, a dual VESC only let me down with the carvon v2’s, because the KV is really high. It’s great for high speeds, but terrible for low speeds. At low speeds, the dual hub motors would make the VESCs over heat after a little over 2 miles of tough, aggressive riding through the hills.

If your doing a belt drive, which is seems you are, then I think a dual VESC 4.12 will be enough for you. If you have over heating issues, you can change the gearing around to solve that pretty easily. Might mean you don’t get the top speed you want, but if you o the math before hand and pick your motors kv right, you can have both top speed, torque, and fun without any issues.


#12

Thanks. This new info kinda tells me that my planned 12S4P LG HG2 is going to lack amps since i will be at the very limit all the time. Need 5-6 and above like in OP :slight_smile:

It would still be nice to see a amp curve if anyone got it with some info on setup/rider as to what I can expect.

It might be a language thing (English is not my first language) but 50A continuous/average at 12S sounds like an extreme. That’s 2.5kW ish and I think I read somewhere that in Tour de France (bicycle) the top riders where putting out like 4-500W while climbing as at a very peak like 1500W. Is these really that inefficient?


#13

I eat tour riders or any spandex wearing cyclist like snacks


#14

Yea, same here. Hummie and I ride very similarly. For some reason, most of the I ride with him, he rides kinda slow for me. But I’m always pushing full throttle when I can when I’m by my self.

My board with hummies motors run 4wd @ 1000 watts each, so 4000 watts max. I fly by spandex cyclists like they are standing still, lol.


#15

A 10S4P or 12S4P will have more than enough power for 95% of the riders here.

When you have a 4P pack with 20A cells then you can use the 80A (4x20A) that this pack is capable of without any issues. You won’t harm the batteries because the only moments you are able to draw that much power won’t take longer than 5 seconds (mostly not even 2 seconds). And all the life time ratings are tests which were done under absolute worst conditions at 20 amps a cell continuously (limit of the cell). And even then the battery’s would have been good for 10000km.
When we ride we use on average less than 10 amps on the entire pack. That is 2.5A a cell for a 4P, not 20A a cell.

So what is the noticeable difference between Li-Po and Li-Ion?
Only at high speeds there will be a difference in the power output. This is because the Li-Po cells will have a higher voltage under load. And also when they are drained till a certain percentage. But the difference is only like 15%. That means that you will have more power close to max speed.
So if your board can do 50 km/h (limited by the kv of your motor) you will only feel a difference of the power output above 42,5 km/h. And you might reach a 2 or 3 km/h higher speed. And that is also only noticeable when you go full throttle.
And your settings of the VESC needs to be high. Otherwise the settings would limit the power anyway. So if you have a dual drive, 10S4P and don’t use more than 30A battery max on each VESC then you won’t really feel a difference
And don’t forget that Li-Po batterys are 50% heavier than Li-Ion when they have the same Wh capacity.

When does Li-Po make sense.
When you are on a low budget.
When you want a really light board and don’t need range. For example for race mountainbaord that only needs to run 5km in a race. Li-Pos are heavier but the pack can be sized smaller.

PS: My watt control isn’t meant to reduce any effects of voltage sag.


#16

Thanks so much for a clear and thorough response!


#17

Well it makes sense that it would though. In current control mode, voltages drops on the battery and thus, watts drop, thus it feels sluggish. With lipos, it doesn’t drop the same and thus, voltage stays higher, watts stay up and every things good.


#18

Current control regulates the current at the motor side, not at the battery side.
As long as the duty cycle isn’t too high (more than 80%) the battery is capable to deliver enough amps so that the VESC can transform it to the wanted motor amps. Only above 80% duty cycle the Li-Po cells perform a bit (20%) better and provide a little bit (2 or 3 km/h) higher top speed. But if you plan to get a 10S Li-Po Battery and don’t go with Li-Ion because of the little performance difference then you should simply upgrade it to a 12S Li-Ion Battery.
This will outperform any comparable 10S Li-Po battery. (I am talking about 4P packs because this is the most used size and provides enough power)
And the upgrade from 10S to 12S is only a increase of 20% more weight. The 10S Li-Po weights 50% more than a 10S Li-Ion Battery when they have the same range.

And don’t forget that Li-Po battery’s are dangerous if you don’t know how to handle them. That is actually the reason i write this, because most of new users don’t know shit about battery’s. (This thread is for those people)

P.S. @evoheyax the graphs in your first thread are very irritating. Because you show the graph of a 2S Li-Po compared to a 1S Li-Ion. Actually you show graphs of a LiFe and LiFePo, so i don’t really know what these are good for.


#19

I included that gif above with your view of lipos in mind :stuck_out_tongue:

If you can find a more accurate graph of a lipo discharge, than please post it and I’ll gladly update it. I don’t mean to be miss leading, which is why I’m trying to have a constructive conversation.


#20

@Ackmaniac when u say 80% of duty cycle why that number…just because the lack of duty cycle’s ability to make useful current and going direct from battery current which occurs at the higher duty/speed requires more from the cell? At high speed there’s a greater draw on the battery w a given wattage output? Seems so
But w 4p ur good w Li-ion and good cells I believe nut it’s just a question oh longevity from beginner perspective. Nicest maybe Li-iron at maybe 14p with it’s great flat discharge curve. As well as so mush more. I’m obviously trying to push Li-iron.