The commercial ones are almost exclusively for charging in parallel not series.
Charging in Series has the disadvantage that you have to plug the power wires and the balance wires in to the correct sockets, or things go very badly wrong instantly, probably breaking the charger, maybe melting ballance wires, and endangering the cell packs. On the plus side, unlike parallel charging you can series charge dissimilar cell counts, ie a 2s and a 4s to make a 6s, and assuming you do plug them into the correct port it is just the same as charging a single pack, while you should only charge packs with the same state of charge, nothing disasterous will happen if you accidentally plug a charged and a discharged pack together, as long (as it is on a balance charge), it will just take many hours to charge and ballance the packs.
Charging in parallel reduces the risk of human error messing things up as it doesn't matter what sockets you plug into (as they are all effectively the same socket), but if you accidentally plug a charged and a discharged pack the charged one will try to charge the discharged one as soon as you connect them, and while the voltage will be OK the charge rate will be almost totally uncontrolled, (I say almost as there is only so much current little balance wires, balance board, and connectors can take), this shouldn't effect the charger as it is happening totally externally to it, but something is going to melt and endanger the packs.
If you use any sort of multi pack charging setup you need to be extra careful, but I think that using a fused parallel balance board, and plugging in the main power leads several seconds before the balance plugs minimises the risk. That way you can't plug the wrong pack into the wrong port, if there is a huge imbalance in the packs it will blow the fuse and give you the opportunity to notice before plugging in the little wires that are in danger of melting, and if the imbalance isnt enough to blow the fuse instantly the charge current has the opportunity to reduce before plugging in the little wires.
Paul Upton-Taylor, Greased Weasel Racing.
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