Using multiple laptop battery packs to power everything
I'd be cautious about hooking them in parallel. According to ADAfruit power leakage between batteries is a problem.


  [multipack parallel] ... batteries are assembled by a company that is experienced and certified to test and assemble battery packs. The individual batteries are tested and sorted by machine so that each pack has matching batteries with the same capacity and internal resistance. Individuals do not have this equipment, which is why you should not try to make your own packs.


Are you certain all your batteries are the same age and have the same usage history? A brand-spanking new one will try to charge an old worn battery to its own fresh voltage.