While the iPad is a very efficient product it consumes more energy to charge it than many boat owners would assume, especially when run through an inverter.
On a small boat with a 100Ah battery bank the iPad could use approx 11% +/- of your usable Ah capacity, when charged via a small inverter. This is of course if we assume the owner is practicing good battery management and only drawing the bank to 50% depth of discharge leaving him or her with 50 usable Ah's..
Total Charging Time = 3:58
Average DC Current = -1.4 to -1.5A
Total Ah's Consummed* = -5.64 Ah (*to when the 100% icon appeared)
If using the iPad while charging it the current stays pretty steady at -1.5A when run through this inverter..
We often have three iPads on-board, plus phones and a laptop computer. The computer is an energy pig by comparison. When you add all these up you can easily break 20-30 Ah's per day if not careful.