You will need to get a 9s bms. The Bestech 10s bms will not work with a 9s battery.
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Thank you very much for taking the time and drawing the diagram! I thought their BMS supports 6s~10s no?
They sell bms’s for all voltages but you have to order one for the specific voltage your running.
here is a link for the same bms but for 9s battery.
http://bestechpower.com/333v9spcmbmspcbforli-ionli-polymerbatterypack/PCM-D223V1.html
And your gonna need a 37.8v charger
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Thank you. Just to be clear, I cannot use a charger that has a higher charging current than my nominal current which is 37.8 Volts?
You can not use a charger with higher voltage than the voltage of a 9s Lipo pack at full charge. Lipo cells at full charge will be 4.2v 4.2 x 9 = 37.8
Just search eBay for " 37.8v charger" I ran the search and found at least three 37.8v 2a chargers
Nominal voltage is 3.7v per cell or 33.3v for 9s
You want the charger to match your battery’s voltage at full charge or else it will not fully charge the battery.
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Gotcha. 
Does anyone have a extra bms
What size?
For those Lipo 10s
I have one I have just taken out if a new build. I’m going a different direction and more than likely will not need it.
I also have 10 2s 5ah 30c hardcase lipo packs for sale. They have been made into two 10s lipo packs. They can be used as two separate 10s packs or wired in parallel for a 10s2p 10Ah pack. This is how I used them and they have been used for 3 charge cycles.
I have a new 37.8v charger in the UK that I’m never going to use if you were EU way.
Holy shit @Namasaki since the last time I visited this thread in January you’ve really had your work cut out for you answering questions! Thanks so much for your insightful contribution! I’ve recently ordered some of my parts now that I’ve gotten around to some extra cash.
Anyhow, I’m running a single 6375 R-Spec on 10s 8000mah and it works great. This new battery setup will be used with the R-Spec but will be switched to the new Carvon v4s as soon as I receive it! My question to you is: would it be better to go with the 12s over this 10s with the Carvon v4’s or is that overkill? Any pros or cons you can kindly point out? Thanks again brotha! I owe you a beer
I think the Carvons will do just fine with 10s. I would start with that anyway.
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Thanks for the quick reply. I do feel like 10S (with Lipos) is very safe. What’s questionable is the 12s with Lipos. I found my motor got pretty hot with a 12s after going up hills. Thanks for the update sir!
I am trying to build a slim board, so I’m considering using 3S 5Ah lipos in series in parallel to make a 12S 10Ah battery pack that can be split across the top and bottom of the board like boosted.
This is the BMS I intend on using: http://bestechpower.com/444v12spcmbmspcbforli-ionli-polymerbatterypack/PCM-D083.html
This image shows the wiring of the batteries a little clearer.
Would this setup work for charging and discharging?
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hi @Namasaki
Do you know if a BMS is supposed to close off a circuit once cells reach a certain voltage? I left my loop key plugged in for a couple days and came back to 1 LiPo completely unbalanced with one of the lowest cells being 1.4v. My other LiPo seems fine since all cells are at my vesc cutoff voltage.
I was under the impression that this was what they meant by over-discharge protection
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can you post a diagram of your wiring? including the brand and model of your bms
Shitty Diagram:
The BMS product page http://www.batterysupports.com/36v-37v-42v-10s-60a-10x-36v-lithium-ion-lipolymer-battery-bms-p-267.html
And also if it matters, how I did my balance connections
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All of your wiring looks correct. However, the over discharge detection for the Supower BMS is too low for Lipo batteries. Once a Lipo cell Falls below 3.0 V it can drop off very quickly. However, the BMS should have shut down when that cell reached 2.9 V