It's a simple thing to figure, once you know the amperage, you can tell how long it will run by the amp hour capacity of your batteries.
Although when you state: "2 14.4 volts 5 amps", it might be confusing for people... and it is technically ambiguous.
First, it's 5 amp hours, not 5 amps...
But is this two 14.4 volt 5 amp hour battery packs in parallel? (14.4 volts at 10 amp hours), or is this two 14.4 volt 5 amp hour battery packs in series (28.8 volts at 5 amp hours), or is it two 14.4 volt packs in parallel TOTALLING 5 amp hours (each pack is 2.5 amp hours).
Makes a big difference, right?
Anyway, for the small smoke unit (this is what I thought the thread was about), it is a 6 volt unit, so theoretically at 1.2 amps, then a 5 amp hour battery of 6 volts or greater (regulated to 6v) would give you a run time of 5 / 1.2 or 4.1 hours if used for the smoke unit itself, or probably about half that if running a loco and lights too.
So maybe about 2 hours of loco and smoke, which is about what was indicated, but I think lotasteam uses the full size 12v unit, which can draw more current.