No, definitely not. I think it is more so the fact that the CPU would never be in an idle state because 'tail' defaults to checking every two seconds, so the CPU will be constantly switching between going idle and then waking, so it could be a battery drain.
I'm no expert in this area so I don't know; maybe a cron job would be better which externally executes the script (but not using the '-f' switch).

Nice job anyway!