Have you considered different hardware? https://en.wikipedia.org/wiki/IPad#Power_and_battery https://en.wikipedia.org/wiki/IPad#Power_and_battery suggests that

Have you considered different hardware? https://en.wikipedia.org/wiki/IPad#Power_and_battery https://en.wikipedia.org/wiki/IPad#Power_and_battery suggests that an iPad consumes ~2.5W (0.5A at 5V via USB). An iPad, or a decent netbook, should be much easier to keep running than your current 60W machine.