177 minutes = 2.95 hours
2.95 hours X 80 amps = 236 amp hours
That's the capacity of your battery now. Check what is stamped on the battery to see what it was when new. Most 3000 pound forklifts with 36 volt batteries are about 600-700, so your battery is not so good and probably only run the forklift for 2 hours.
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