I sat down and was looking at the laptop I use today (dell inspiron).....the power cable says 19v at 4.2A too, but the internal battery is 11.1v. I think the AC adapter pulls more power to charge and run the computer...double check (I use a 12V to power mine). I don't know what type of batteries you want to use, but I use NiMh from batteryspace.com (4000 Ah sub-cs). Sub-C batteries output 1.2V (2 in series 2.4V, 3=3.6, etc.). Hope this helps.