On FlexiBMS (and most other BMSes I assume) you have to first connect the negative ground terminal of the battery (0), and only then plug in the balance wires. When disconnecting, vice versa – first disconnect balance connector, then main terminals.
I like BMS to act this way, it forces proper safe procedure when disconnecting to fix an issue with the battery. Here’s a scenario I’ve personally gone through:
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I mess up in the building process and one cell in a p-group isn’t properly welded, leading to it being disconnected
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I notice this when charging and discharging the pack, so I go to remove the affected p-group
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before desoldering anything, I first remove the balance lead from the BMS, this is important so you don’t have to worry about damaging the BMS when desoldering things. this will also cut power to the BMS (as now the only “live” connection is a single lead from the negative of the pack) (only when not using BMS discharge)
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I am now able to safely work on the pack without fear of damaging the BMS or shorting things by accident (while the risk is always there, there is slightly less of it now)
Hmm… i wonder why that is. Maybe the balance connections are connected electrically within the BMS somehow.
Do you have a source for that? I’m curious.
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Progress being made but can’t discuss things yet…sorry.
I love that…it’s a brilliant idea. But it would be hard and expensive to do.
Each balance lead is a certain voltage above BAT- (ground for any electronics) and possibly “mixing up” the balance lead sequence means that every connection point would need to handle up to BAT+ because you would never know where the top balance lead would be connected. This forces up the cost of the components.
If we force balance leads to be in order then the biggest different between one lead and another is just the voltage of one cell.
Another huge issue is that if balance leads are randomly connected then the balancing is done for random strings of cells. For example, if we have BAT- for the lowest balancing connection, then cell 5 for the second connection, and then cell 2 for the third connection we have a problem.
Each balancing point drains current between the two adjacent connections. If the connections are in order that’s great, it’s one cell per connection.
But in the example above the second connection has five cells across it. Even if we can handle that higher voltage (as discussed above) it means connection two can only balance (drain) cells 1-5 all at once.
It’s the same issue for connection three in our examples above…it would balance cells 1-2 at once.
With random connections we lose the ability to balance individual cells. This could be fixed with a ton of extra circuitry or with completely isolated channels but that would be pretty expensive and large. 
It’s not too hard to allow balancing connections to be made in any time order (but still in voltage order) as long as the main pack negative is connected first. Well, for my BMS’ it won’t matter. For some on the market it might matter a lot or they are just being conservative.
Most electronics just hate not having their ground connection in place before handling any voltages. It’s the “reference” for any voltage-related decisions it needs to make and is required for any electronics to operate properly and in the expected way when other voltages are connected. @sleepless
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Dammit…ya’ got me thinking about this now and wondering if there is some kind of circuitry fooling around that could handle that for us. Too great an idea to just discount “because it’s hard”. 
A large solder jumper-pad matrix on the circuit board would allow random balancing connections to be routed to the correct BMS input but having 144 connection solder points to route a 12S pack’s balancing leads would be a disaster IMO. So easy to mess up and short-circuit cells by routing them to the same input.
There are multiplexer chips created to electrically route signals but we’d need a lot of them, a microprocessor, some buttons, and a display in order to choose which balancing connections go to which BMS inputs. Would be very cool to see but also big, expensive, and still prone to error.
We need that auto-routing of connections you were thinking about…somehow. 
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I hope figuring out a solution to this won’t keep you up at night lol
It certainly is an interesting problem to solve
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Might as well ask for a bms to connect your p groups in series, and cut you nickel 
There are some “balance wire cheker” jigs out there with LEDs already
Handy thing to have
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