There is nothing inherently wrong with series charging. Consider that any multi-cell pack is being charged in series up until the balance portion of the charge. The "s" in the naming convention stands for series. The problem with charging these hard cased shorty 2s packs in series is there is only one independent balance lead, so you will need to build an oddball charge lead. It's possible, but TBH, pointless, since charge times will theoretically be identical (you'll save time not having to swap the packs though).

It's much easier with more standard type battery packs that have completely separate balance leads, assuming you also have a charger that can handle the new cell count.

Another thing to keep in mind is what your charger and PSU can handle. Lots of folks are near their limits charging at 40A. If you are near your limit at 40A and you double your cell count, you will now have to cut your charge current in half.

W=A*V

2S 5000mAh pack @ 2C is 8.4*10=84 Watts
4S 5000mAh (two 2s in series) @2C is 16.8*10=168 Watts.



To reach your goal here, you do not need to charge those packs in series.

I think the reason we don't see series charging multiple packs very often is because:
-There is no benefit
-In many cases, the resulting cell count will exceed the rating of your charger. Not the case with running 2p4s saddle packs, but it would be the case if you were to run 4s2p saddle packs.

I think maybe there is some confusion there. You cant properly balance a pack when parallel charging unless you independently balance the pack after the charge cycle is completed. It's impossible. When parallel charging, each balance lead splits into two cells which the charger sees as one cell, so there is no way it can accurately balance both of them. The general rule with parallel charging is, you should give them a normal balance charge every few cycles in order to balance them properly.


EDIT: IDK, I'm not buying it with that article. Most of it is great advice, but the parts about cell counts don't make sense. We have been using HV LiPos in series on RC helis for more than a decade. No problems such as what is described in that article. In theory, these would be grossly evident with RC helis. We pull 8000mAh in 4 minutes running 12s 6p2s saddle or stick packs. A 6s pack as what they describe is six cells in series. Assuming what is stated was true, then we would be seeing single multi-cell series packs also fail in the same way.... but we don't. Two 3S packs in series is the same thing as one 6s pack, aside from the added resistance you may get from the jumper.

The bigger issue with running series packs (especially stick packs) is the added ripple current you will see due to the extra-long battery leads. Capacitor banks help smooth that out.