Battery help - combining packs

Ok - Will somebody with more experience tell me if this is OK?

I’m considering using four different packs of 18650s that I already have

2 packs are 5s3p
2 packs are 5s2p

Can I parallel one 5s3p with one 5s2p to make a 5s5p - then do that same thing with the other two and have two 5s5p packs that I can plug in those and get 5s10p

Packs will not be split apart - each of the four would plug into a connector so I can still use them for what they came with. Each pack has a built in BMS.

I think I can do the above - but I don’t know what my limitations are and what to be careful of. I’m pretty sure i have to charge them all full first - and connect them in order. . .

The other options is to just but four new Lipos for 12s2p and a new charger for them - which would be much more expensive but would get high discharge which is what I want.

Be very careful because mixing batteries can be dangerous. However it should be fine if the cells are all the same capacity and close to the same number of cycles because if some of the cells have less capacity than others you will kill the cells.

Thank for feedback. They are not the same capacity. 5s3p and 5s2p. That’s why I’m worried.

Also - I plan on being careful - but not sure what being careful actual means

Do you know what kind of 18650 they are? If there are both 30q then the individual cells that make up the packs are the same capacity and you shouldn’t have a problem as long as they are also close to the same number of cycles (It doesn’t have to be 30q it could be 25r or what ever other 18650) but you can not mix a 30q and a 25r. Those are different capacity. 18650 is the size not the chemical make up.

It’s a bad idea, it’s already difficult to maintain all pgroups balanced with the same cells, it will be almost impossible to have random pgroups balanced. If you go ahead with it one of the pgroups might drift during charging until it explodes, a burnt house is not worth the risk of the savings


Thanks for the feedback guys - I sure wish I understood the details better. . . .so I can break,bend, or follow the rules when I want to and know exactly what is happening and the risk. . .

Looks like i’ll be buying lipos and a charger. . .$400. . . big thumbs down. . . just not as satisfying as buying gear drive,wheels, even VESC

I do not agree with other guys.

If every pack has its own bms and they are all same S count (5s), there should be no problem connecting them in parallel. Each pack will be protected with own bms. It doesn’t matter how old are cells or if they are different or not.


I have three other websites open shopping for chargers and lipos. . . .now you throw this wrench in my plans!

Actually it’s a very interesting wrench and I’m glad you threw it. much more intriguing to try to make these existing cells work.

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You can connect them in parallel, no problem. But if you plan to connect them 2 in parallel and 2 in series to get 10s5p, then you could have a problem.

So you want to use 5s battery in esk8? And you are thinking about buying 12s? Difference in top speed will be humongous. I even think that 5s will be unusable how slow it will be

Yea - planned everything around 12s - gearing, motor, etc. Then this idea came up to use existing cells.

It’s for my kid and was going to limit speed in vesc - but I put 5s10p in calc - and I can get 15mph which is more than enough for him.

Will running such low voltage be difficult for motors and VESC? I’m thinking about buying two trampa vesc6-3

I had also considered the 10s5p and wanted to try both ways - in my head it makes sense - if I parallel the batteries first than I should be able to connect two different 5s5p packs either way right?

5s for a kid is good idea, with top speed of 15mph I think its enough.

Your kid is probably much lighter than you, it should be no problem for vesc. Btw low voltage will never be problem for motors.

I think its crazy to buy two best and most expensive vesc for 5s board. Big overkill. Go with something chepaer, makerX dual or even 2 single flipsky 4.12

You CAN connect them in series, but both 5s5p has to have same cells (or same cells mix) and same capacity. If they do, put low voltage cut off in vesc settings on much bigger number, and check if voltage difference between first two batteries (5s5p) and second two batteries (5s5p) is big after ride. You will still have to disconnect them after ride and charge them with 5s charger and then connect them back in series when they are on same voltage. Why is that? When you connect them in series, vesc will see 42v when full (sum of first 5s and second 5s) and after ride, there is big chance that first or second 5s group will discharge faster than other. Vesc will still see sum of their voltages, but there is chance you trigger low voltage protection on one bms and that will cut off voltage from your vesc and that won’t be good. That is why you want low voltage cut off set higher, if you still want to risk it in series. Hope this all makes sense :slight_smile:


As others have said,
connecting cells in parallel should be fine, as long as the voltage is the same when you connect them, even if the capacity of the packs are different.

Connecting 2 packs in series should also be ok so long as the capacity per cell is the same and they are a similar voltage per cell.

Maybe some pictures of the batterys would give people a better idea of what your trying to do.

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I chose the trampa vesc6-3 because I had planned on 12s2p 75c lipos and I wanted high amp - had previously settle on the flipsky dual6.6plus but at least 50% of comments about flipsky are bad. Before Flipsky planned on unity but that didn’t work either! Maytech seems so-so. Some cool new VESCs being developed - which is great for later this year. I have no experience with any VESC - just trying to glean info by scanning a million threads (which isn’t easy for a novice btw!)

Basically I planned the entire build around high amp high torque. trying to make a burnout machine.

also- it’s for my kid - I just wanted to be able to have a “dad” setting for me to have fun too.

Thanks for taking the time to comment - extremely helpful to get any sort of feedback

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I thought you want to build two separate boards. But you want to share board with your kid, nice :slight_smile: In this case, go with trampa vesc6 - you can’t get anything better at the moment.

As far as I know, you can change profiles in vesc android app, so you could limit top speed there for your kid.

I see another problem here - 10s5p is much physically bigger than 12s2p (ok, you didnt say how big are lipos) - and there are 4 bms instead of 1 in li ion pack… I mean it all depends which deck you use and if you want to top mount box and put batteries there, but either way you should plan enclosure to fit those 4 li ion packs.

No problem, glad I could help :slight_smile:

been looking at makerx - thanks for suggestion - hadn’t looked at them before.

I like this one. . . X-ODRIVE UPGRADE! HARDWARE VERSION 3.6 $185.00

I’ll do a search and see if it’s a winner.

Don’t get that one, it is not based on vesc. Get something vesc based, you don’t want anything else for esk8! (At least for now)

yes - I see my mistake. stumbling my way through this. . .


This entire project has been difficult to “package”. It’s been my #1 time consumer

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Maybe try top mount box? It will be much easier to charge/replace packs