Range Extender))

Hi guys,

So I am building a 12S5P, 20AH DIY Lacroix as stated in my build thread.

However, i think the range will not be enough, and am looking to build a range extender to put in a small box on top of the deck and connect to the charge port while riding.

Do you guys have any tips, would double range be expected?

What batteries would you use?

I have no idea on how to make one, need some ideas please.


Use the same cells in 12s, p count does not matter. Your charge port should be able to deliver the current, e. G. Xt90. I recently did the same, doubled a 12s3p and connect it through qs8 connector.
Take care that the voltage of both packs is as close as possible.
Edit: of course the cabling involved needs to be able to handle the high current as well. Awg10 in my case.

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Do you need a way to limit the amps?


Thanks mate, can you provide some more info please? did you have to use any step down converters?

How did you limit the charging current?

I will be using a smart BMS which will allow charging current limitations i believe, maybe that could work.

Also, how do you charge your range extender via balance charging? using liions or lipos?

But how should us non-smart BMS users do it? I have a 12s 9Ah pack so I could do with another 12s 6Ah box for long rides

good info here


For a street board, a pelican like case with a clip base filled with a voltage matched pack and a step up to counter the voltage sag?

Can you put the step up on your main pack and never get sag?

No step down converters. I don’t charge during the ride, I start with both packs at the same voltage and connect them in parallel through my oversized charge port so they are basically one big battery (12s3p)2p :slight_smile: Both batteries are balanced charged first and need to be at the same voltage (as I wrote before) During use they discharge evenly, any difference will be balanced by themselves.
If you want to charge your main pack with the other you need to check for the linked thread.
For short there are 3 versions of a range extender described there:

  • the thread started with the approach to connect e.g. 2s to a 10s battery in series of the loop key port. This creates a 12s battery where you have to take care that both packs never drain to much. In my case I used a 2s Lipo Pack with 8Ah to boost a 10s3p Liion pack to 12s. The main battery was a bit bigger in capacity so I used a lipo warner for the booster pack.
  • Second: I you want to use another battery to charge your main pack while driving / stationary you need to use a step up converter and a charger (as far as I remember, this was not my way but is described in the thread)
  • Third: Connect a pack in parallel with exactly the same voltage over the charge port (High current)
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Hmm, i’m not sure this makes sense. The sag will be distributed over both packs in parallel (and reduced because of that)

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Isn’t the charge port not parallel since the negative isn’t common?

If you plug into the charge port, do you need the extra pack to be 4.2V times the series count or just higher than the main pack?

Basically what happens if I plug a 49V battery into the charge when the board is at 45V? (12s)

That depends on your setup of course, if you use a BMS the other battery has to be in parallel to the discharge lines of the BMS. I balance both packs externally so its easier for me. (Charge port == main battery connection)

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So you have 2 charge ports? One connected to the BMS and another that’s just a parallel splitter with an anti spark?

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Uh, don’t know, I read about the voltage difference mustn’t be greater that 1 Volt, although I think that was for smaller packs. In general the closer the better :slight_smile:

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Closer to full charge or matching? (For BMS charging, I know parallel packs gotta be same voltage)

voltage of both packs as close as possible, state of charge is not so important.

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I use no BMS since the ones suitable (High current discharge) would be way too big for my setup and a external balance charger works better and more transparent than a charge-only BMS.


For a pack you can connect any time (even with the main pack dead and extra pack full), do you need this step up?

I’m thinking of a 12s2p with BMS and a 15A booster in a hard case that I can clamp onto the board on the go or charge from a car

This route is well documented in the thread @sk8l8r posted :slight_smile: