Watts = volts x amps.

So, 1800w divided by 48v = 37.5 amps.

Most batteries list maximum continuous current (amp) ratings and "short-term" or "peak" ratings. These "peak" ratings are sometimes measured in very short durations (i.e. a few seconds), or (with higher quality components) as much as 30 seconds or more.

Manufacturers will sometimes try to make their product "look better" by making absurdly high "peak" amp ratings that are based on a duration of just a few seconds.

Anyway, I usually try to select a battery/BMS combination that offers a peak rating that is no more that about 2-5 amps beyond the battery's maximum continuous amp rating.

HTH