cron insists on running makewhatis and prelink, two processes that cause intensive disk activity, regardless of whether the laptop is connected to AC or not. While I like prelink, I don't like it nearly as much as having a low power drain. IMO cron should check the AC state before starting jobs tagged as power hogs. It should defer them when on battery power. And run then once AC is reconnected.
This is now checked between anacron started running jobs. If laptop is on battery, then the job won't be started and anacron will try next hour.