ISTR that lead-acid batteries weren't allowed on planes - tickets say "no wet-cell batteries". You may need to go for a NiMH/NiCd solution.

In my experience (United, BA, Virgin) you don't get laptop power feeds unless you're in business class... which I only ever get to go in if they accept bloody air-miles upgrades on my ticket type (which invariably, they almost never do).

If you can get mlord to add it quickly, a "display off" setting in hijack (actually turn the display totally off, back to blinking LED) this will help your battery life a lot - it's the major power consumer in the system.

Hugo