Personal experience speaking here guys......
When charging multiple 3-6S packs in parallel, be mindful of using them in a series connection, ie 2 6S packs in series to make a 12S pack. If the cell voltages are not equal to another, you will end up with a cell or more greater than 4.2V. I seen this over the weekend as well. I charged several 45C Pulse 5000s 12S stick packs f9r a guy, and he was parallel charging each stick pack. Not only does it drive up the IR somewhat, but the above mentioned. His packs were turning around for a healthier discharge after 4 cycles.
If charging in parallel and only using each pack as a 3,4,5 or 6S pack...... It is ok, but every once in a spell, use them a few times and charge them indivudally.
When I got my iCharger 406 Duo, I went from parallel charging to charging as 6S packs, each port, not only did my packs IR be reduced, but the cell voltages are always within 10mV of each other, low to high cell. I now have gotten another iCharger, a 308 Duo. I need more power to run both supplies at their peaks. I want 3500 or 4kW supplies. But then, I need more genny power too. All in due time.