this web page runs locally on your browser on your machine, no data is transmitted to a server unless you use bookmarks. then it submits to same page (nothing active on server side) and builds a URL. it's just a simple calculator I have made provisions for making the values bookmarkable if you wish to share the information.
Ah (amp*hour) and mAh (1/1000 Ah) is a measure of power a battery can deliver on a charge.
some generators have a battery. the battery output is connected to a voltage inverter which runs your device (well, there's also a charging circuit, but we are ignoring the charging circuit in this calculator since it's not relevant to what we are trying to find which is the running time you can get).
the sample application for such a generator here is for time lapse photography if you have a camera that supports that video feature.
to specify Ah, put in a number like 40Ah. to put in mAh, put in 2000:mAh, this takes SI and IEC units.
for Volts, put in 1.2VDC or 12VDC, or for VAC put in 120VAC or 240VAC.
firefox is the best browser to view this with, since it implemented MathML in HTML5 like they should.