They each have an AMP hour rating.
20 amp hours means that they can power a 1 amp power supply for 20 hours.
Most laptops are from 2-4 amps so you would probably want one to give you 40-60 amp hours to get 20-30 hours of recording time.
As for the motu, it is very good stock but if you want to make it even better, Black Lion Audio (search them on GS) modifies the input stages to make them sound even more open.
Independent Arranger / Producer / Engineer
Chicago, Il 60622
(Nuendo 3, Native Intsruments, lots of other software synths)
disclosure: I work at Guitar Center but do not speak for them unless otherwise noted.