Hi Andy!

I think your'e saying the batteries are getting hot after 5 minutes. In that event, charging 2 packs in paralell would split the current to each pack in approximately half, with the same voltage to each. BUT, depending on the state of charge on each pack when you start the charge cycle, plus any mismatch between each of the cells in either pack, you would be unlikely to get them to charge equally and "peak" at the same time.

Just my thoughts.

Russ