What's your experience with external battery packs but for laptops not for smartphones or tables? Are you better off buying a whole new extra battery for your laptop and not wasting your money on external and more universal battery packs? This only if your laptop allows you change and replace the battery so Macs are out of the equation, perhaps that's why the only models of external packs that I seem to find are for the Mac Air. Having some extra battery juice for emergencies sounds nice but I don;t know if the technology is there yet.