No longer battery life at all!
and here's why:
A battery pack for a 36V system contains THREE 12V batteries (let's just say 60Ah each)
drawing 1000W @36V continous means you have 2.16hrs running time;
with a 48V motor you will have to use four batteries (still 60Ah) and true you'll have a 2.88hrs runtime;
BUT that one battery still has to be considered in the 36V system (although not present);
So let's assume we add a fourth cell in parallel to the first batpack,
instead of 12V 60Ah it's 36V 20Ah (which is the same amount of energy)
and those 20Ah is exactly what's needed to increase the runtime by 0.72hrs to 2.88hrs.
So... no.. same energy; no real increase in battery life
In fact that one battery will add weight, thus more power is needed to propell the kart and in the end more power drained from the batpack
So you will need one battery more, and THAT increases the capacity and thus runtime;
you will use the exact same electrical power of course
But lower Amps are indeed a bonus,
first: it's the Amps that will kill you in case you get it touch with electricity
your doorknob for example can deliver up to 40000 Volts, and is perfectly harmless;
a car battery has 12 V and can kill you in an instant.
So low Amps is safer than higher amps.
Also electronics to handle big amps are more expensive than those which can handle high voltages.
So lower Amps are 'cheaper' to control.
And last but not least, there's basically a sweet spot for a specific voltage/amperage motor,
the one where it has the best efficiency.
High torque motors run better on low voltages and high Amps (lower internal resistance)
High speed motors better on higher voltages and lower Amps.
But since you need both (torque for a good acceleration and high rpms for speed)
that's not really important for a car just for motors in industrial applications (constant speed applications)
'sid
)