What type of Battery? How many hours is a few? How high do hey lift? How far do they travel? Are these the only three units in the freezer? How many shifts?

You can plan on a 110 - 150 amps per hour will be used per hour of operation (680 amp *80% = 544 amps available, 544 / 150 amps = 3.63 hours). so if they use 1200 hours a year or 3.29 hours a day, they will change a battery every 1.11 days per unit. I would find out the actual amps used per hour and usage then you can be more exact. Based on this you do not have enough batteries on the shelf.

Good luck