There is always a option for BMS Like this one http://www.batterysupports.com/lion-lipo-nbsp-36v-nbsp-10s-c-32_41.html
If you really want to use the parallel/series switch, here’s a way to double the capacity of your switch.
Use a 4PDT switch (4 pole, double throw) instead of DPDT. Then split each of your leads in parallel across two poles. This effectively cuts your current in half!
https://www.amazon.com/4PDT-Heavy-Duty-Toggle-Switch/dp/B001TJ6O9M
wel i will just go wit my 2 key disinge
I’m going to use the same idea of the switch circuit with xt60/90 keys. Here it is: the Ps stand for parallel, while s stands for series.
i dont se any problems the circuit but this stil wil feed power to ur ecs /vesc
Series/parallel switch, I’m really inspired by @kaly’s switching. And I know his experience has been good. I want to believe! But…
Those cheap small switches have 2 challenges. Current/heat, which has already been discussed, and arcing.
Appears DC arcs way more easily than AC. I think you can step around this using a loop key to open the circuit before switching. That adds one more step to the dance. And the switch may still arc because the contacts are so close.
I’m also struggling with a high current on/off switch. Don’t want to pay $60, don’t want to go solid state. Antispark loop key looks like an okay solution, not great. Marine DC circuit breakers (with arc suppression), I maybe be wrong but I don’t think circuit breakers are designed for many on/off cycles.
And BMS, if I could buy one from a non-china based company who can be held accountable for failure, I agree, this is a good way to go. But with the sources we have for diy, seems like a gamble. I know some vendors have established at least a decent reputation, still I feel the sample size is small. And you might not notice your BMS had partially failed and is killing one or more of your parallel groups. Some of these packs are like $500! I’m too paranoid…
But maybe @JTAG will save the day!
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This is a good perspective on the matter.
Welcome to the nuance of DIY uncertainties. 
Yeh I always thought it would be problem with BMS monitoring the parallel groups. Seems like its not very reliable… You really still have to go in with a voltmeter and check every cell once a month to make sure.
Here is the completed circuit with the series/parallel system built in. I also added lights for night riding
You cannot glue the two plugs together. If you attach both plugs at once you will have one series and one parallel connection which will lead to a big meltdown…
nope that is not true just dont connect the plugs
rip post 
The wiring is correct 
Only remaining problem:
If you attach the Voltmeter before any switch they will be turned on all time… if you connect them after the series connection you dont get individual measurements…
that can be fix wit a very cheap switch 20v 0.1a like this one http://www.qspproducts.nl/schakelaar-flip-over.html#.WCQ7jDvObgI
What voltage are your batteries? Because with this configuration, your lights would be seeing the full pack voltage. You can’t just connect 12V LEDs to a 50V source without expecting a fireworks show in your mom’s basement 
Your right, thanks for pointing that out? Any suggestions to reduce the voltage there? I don’t think run of the mill resistors would work… If it is too big of a problem, I’ll either just make a 2x AA separate circuit for them, or just remove them completely.
Buck converter
18650 !!!
Yet another evolution of the circuit. This one incorporates the BMS and a permanent series connection. While at first I was a little skeptic about the BMS because of so much uncertainty over the internet, I found a reliable source, Battery supports.com, and felt more comfortable. This design, instead of having like 7 ports on the parallel/series circuit, has a power switch and is charged by laptop charging brick. I think the slim uncertainty is worth the sacrifice for the convenience. Also, there is a switch for the lights. As for them, I’m using a 6 led, 6.2x1.7 inch flood light bar, and a buck converter for the voltage reduction.
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