Originally Posted by topgearuk
Is there a limit in voltage difference using same cell count packs that can be connected? i.e if one 4s battery has 20% and a 2nd has 80% and both are connected to the board.
As far as the MPA goes, it won't be possible to cause any damage to the unit, the wiring, or the charger to which it is connected by intereconnecting batteries of vastly different charge states.
However, as far as the batteries go, it's a good idea for the packs to be of similar states of charge. There are a ton of threads in RCG and other forums that discuss this topic. Our observations have shown that no matter what the state of charge, the initial surge currents which flow from a "full" battery to a "dead" battery are not as large as one might think, and the duration of high-current, un-regulated "charging" generally fairly short; e.g., even at 80% and 20% states, you're likely looking at 10-20A for a few seconds, followed by 5A-10A for 1-3 minutes. Whether that's enough to damage your batteries depends on too many factors to discuss here. It seems obvious that a 10C-charge-capable LiPo could withstand it better than a 1C capable LiPo.
Most would agree that if the individual cells are within 0.1V, it's a good rule of thumb and safe for pretty much any LiPo battery, although that value could be a bit overly contstraining, in my opinion.
Hope this helps!