If the components, in this case the batteries, are in parallel then the voltage is the same.
So true, one battery pack has higher capacity. But because it provides less amps its capacity will not go down as fast. The system will regulate itself.
Ok, thanks for input… now we need someone to test this out!
Agreed, now back to @edwardlui531 for some testing.
And to answer your question, I think paralleling the balance leads would help stabilizing the battery system.
Electrons stream from neg to pos but Current flows from pos to neg. It really does matter because it is important to know what direction current is flowing. For example, when deciding where to place a fuse.
So, have you tested your theory? Or can you provide some other evidence that proves it?
your theory seems to suggest that the internal resistance regulates curren flow. I don’t believe this is correct. If it was, then C rating wouldn’t matter at all. And a battery wouldn’t explode when shorted with a wire because the internal resistance wouldn’t allow current to flow excessively. I’m sorry, but in my opinion, your theory doesn’t seem to hold water.
C rating is a function of internal resistance. It’s used for convenience because most people can’t deal with internal resistance.
I believe my theory is correct and I could provide more evidence by providing more calculations.
But I can’t … Because I have to go ride my board until my Akku is empty and I can’t post here while riding… 
Thank you for the input, that is exactly what my theory is 
now, do you think I can add a resistor to the liion pack so it will never exceed the amp draw that I wanted? or is there some sort of special resistor that only limits when it gets to certain current?
Guys, I still start by testing the internal resistant of my pack.
And I have to admit that I was wrong …
… I am able to post while out riding.
All the other stuff was correct - of course.
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http://diydrones.com/m/discussion?id=705844%3ATopic%3A1095758
The end of this says the internal resistance and lower mah pack can balance as the resistance will reduce draw from that pack regardless of c rating
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I hope that ‘‘Roger Sterling’’ from that diydrones.com topic does not mind, that I quote his contribution to this topic. So here it is goes (for the benefit of continuing this thread and educating others)
Roger Sterling, Dec 21, 2015, diydrones.com: ‘‘Different batteries in parallel?’’
A very accurate model of a battery is an ideal battery in series with a resistor equal to the batteries internal resistance. When under an external load the voltage at the battery’s terminals is the no load voltage minus the voltage drop across the internal resistance.
For batteries in parallel and under a load, it is the terminal voltages that must be equal. This will differ from the no load voltage ( ideal voltage). For two batteries in parallel with the same zero load terminal voltage, the ratio of the current supplied when a load is switched on by each battery would be the inverse ratio of the internal resistance.
The instance a load is switched on, the battery with the lowest internal resistance would supply more current and this has nothing to do with the batteries capacity. Depending on the capacity of each battery, it’s contribution to the total current, and the discharge characteristics, the no load voltages difference (Bat1 - Bat2) could be positive, negative or zero.
Statements:
As long as each Battery can handle the entire load without damage none of this imbalance in discharge rate really matters much until one of two things happens. 1) The load is suddenly switched off 2) One of the batteries reaches it’s full discharge voltage before the other.
Situations:
In case 1, each battery’s voltage will instantly increase. I measured this increase on 4 parallel 18650’s under a 1 amp load to be about .2 volts. Each battery in a parallel pack will increase in voltage by the product of their contribution to the previous total current times their internal resistance at whatever SOC, they are at. For different battery types there will no doubt be a voltage imbalance and current will surge from one battery to another. The higher the previous load current the higher this voltage difference will be. If it were only .3 volts and the combined internal resistance of the batteries was 50mOhms the instantaneous surge current would be 6 amps, which may exceed one or both max current rating. Of course this current would discharge one and charge the other and rapidly balance the batteries. But there is a slight potential to cause one or both to suffer a capacity – Case 2 can have devastating impact on a battery. Say one battery safely can discharge down to 2.8 volts and it’s parallel partner can drop to 2.5. If there is no protection circuit the 2.5 battery will happily continue to drain current into the load after the 2.8 is already in dangerous territory. The best solution is individual protection on each. The parallel pack could share a single protection circuit that shuts them down above the 2.8 volts. There would be a loss in usable capacity of the 2.5 volt battery, but at those voltages it wouldn’t amount to much.
Conclusion:
A good rule of thumb is to try to use batteries of near equal capacity and similar internal resistance.
If you do use different capacity batteries try to make sure the smaller one has a higher internal resistance.
Example: 1/2 the capacity with double the resistance. This will make sure each battery follows the same discharge curve and the voltage surges from sudden load change shouldn’t be a concern
— might be slightly different than the topic —To be very honest with you guys. I agree that if you run VESC monitor mode, you can see the peak current draw of a motor would be around 20A - 40A. That means 10c - 15c battery from a 5000mah pack would be good enough. This is true! however if you try buy those 45c battery or setup some more parallel batteries, you will see more power could be delivered to the motor. You get more aggressive respond. This just a FACT! you can roll whatever number there is, but the truth is the higher c rating improve performance to a certain point around 65C 5000mah (more than that) doesn’t do much improvements.
So that brings us to the point, that it’s just not going to be as agressive / fast as it could be (2 batteries with different c ratings)… I suppose
Trust me. If you ever go racing with same board on same track. I guarantee you the higher c rating battery wins. It gets you accelerate faster, those burst of energy when acceleration are provided by the batteries, not the esc.
Well if you confuse with all this mixing c rating, theres a simple case that might help you clear out why it’s actually okay.
You have several batteries of 5000mah 20c rating connected in parallel. Lets say one of it is damaged, so it can only store 4000mah (memory effect / other cause). Although the c rating stays the same 20c, but different in mah means different max discharge capacity. The board will still runs… ofc with the fact that if you throttle up / accelerate, the 5000mah 20c battery will do most of the heavy lifting.
Any how anyway, why do you want to mix - match different batteries in the first place in order to get best of both worlds? the benefit is so insignificant compared to full lipo or full lion. Mix batteries makes your build more complex and charging is more complex, which may is prone of breaking.
If you think lipo is super cheap but cant quite bear the low life cycle, then add more lipo in parallel. The least you put the battery under pressure / heavy load, the longer it live.
If you think li-ion is better in terms of life cycle, but poor in discharge, then please add more li ion in parallel. The more the parallel connections, the higher the discharge capability.
Stop making yourself too difficult 
I think the point here is in utilizing / using the low discharge batteries (if you have lots of them), that way saving the lipo’s a few cycles or improving your ride distance… Otherwise, as always, if you have shitload of money and can build a high quality / premium cell, do it that way…
There will be always someone who will see the bad sides and good sides… mixing of both worlds, at least in my case, just means that you don’t spend, say 200$ for new batteries, but use the available ones (40$-50$ value?)… and try to make the best out of them… not saying it’s the best option or whatelse, it’s just gaining some experience (like building a low grade battery first) and testing out what comes after… if it’s a crap / waste of time… then gladly someone will come to this realisation and post it online for others not to try it…
not saying it is the best option,… it won’t be, if it won’t work, just ditch it, use these batteries elsewhere and think about ways of gettings hands on some good cells / pre made battery. It’s the idea about being able to use lower discharge batteries and still gain some benefit from them… Are they 100% up for this application? not quite… Is it possible to at least get mild / average results? Possible yes…
Ok, I think you should have got my point already… It’s just a matter of perspective / resources and motivation to try something out.
I think they should work… You won’t get as much power as from lipo’s, but you should be able to pull, let’s say these 400-500w out of them, and if they do work in parallel with lipo’s, that may improve their chances even more…As someone already suggested, peak amp draw was around 30-50a… So, if you do use your board only on flats and don’t speed it / accelerate it nonstop, you should be able to get at least a mildly satisfying result… Some people are still using lead acid akkus. (e-scooters, old type e-boards)… their distance and speed sucks in comparison what ppl achieve with lithium akkus… but there were and probably still are ppl who use such tech.
It is a matter of application and experimentation. I still have not seen a comprehensive chart of how many amps does a motor / system needs, at what movement speed, rider weight, wind speed, rolling resistance and other parameters.
After thinking about safety and practicality, I think I am just going to build a 18650 battery bank and have a switch to charge the lipo when the lipo is low. But no charging while riding since I think that will kill the lipo even more.
Kinda like how you carry a battery bank for you phone when it runs low.
My dad even have a crazier idea. Having a foot switch that switch to lipo, kinda like a turbo. Thats sounds too cool
I think the idea is not that bad, only downside is that, it is recommended that the li ion pack has lower capacity than lipo’s, for it to work great, at least that’s what Rogers from diydrones.com recommend.
If you do use different capacity batteries try to make sure the smaller one has a higher internal resistance.
Which makes it kind of difficult to implement, since it would be easier the other way around and build a larger liion pack (low discharge, lots of extra batteries, if they come from laptops).
If you do come closer to making some of this work, report back so we know how it went!
this is why I might add a resistor to limit the current
http://www.rcgroups.com/forums/showthread.php?t=733543
Someone tossed in another idea - to think about cooling.
And someone also told that these discharge rates seem to be conservative, which just means, that the battery will be able to put out more amps, perhaps won’t last as long (higher discharge, lower capacity).
I think if you can push out similar life cycles out of li ions compared to lipo’s and you have gotten these batteries for little cost, then why not… (another point, why try to make this work)…
So yeah, we are not the only one’s who have though about doing this…
Edit: Another resource, where it seems someone has already done this:
(have not read all of it yet)
This last link is about mixing in series, which I’m doing with 5ah 30c and 4.5ah and 90c. 12s, 3 and 9, and can’t find info on this connection other than the one u also found. I think I’d be ok in parallel right? Nothing gets warm.