Yes you can-wired in series so the cell count will be the total with voltage to match, but it will be same size pack. Do not try with pacs of 2 diff capacities. These should be as identical as possible.

Unless these are well matched cells and built in a side by side configuration (sbs), you'll find they won't charge as well together as a 12 or 14cell pack. If they are sbs and you discharge them to identical voltage with an individual cell discharger, you increase the odds of geting a good charge. But practically speaking, if theyre' not matched, not sbs and not discharged to same voltage, you'll get a better charge charging them separately. Get a 2nd charger - thats what I did for my Emaxx.

I've tried it with stick pacs, there always seems to be cells that are slightly out of balance with others and this makes for uneven, incomplete charging. You'll prob see one pac getting hotter than the other. With a stick pac, all you really know is the total voltage and its rare that all cells in the pac will be at the same voltage with the same internal resistance.

If you're racing, its once a day to get the utmost out of a pac. Bashing - I run mine as many times as I want/can. Let them cool like you said and charge and run. I also limit charging to about 1C - 4400packs gets charged at 5a, but I monitor how hot pack gets as it gets close to peaking. I don't let mine get over 135F - high temps tends to shorten batt life.