i've seen a few of my customers that have used electric's on ramps.
They do have a tougher time doing it and yes, it will eat up battery power quickly especially if the ramp is as steep as you indicate. Will it do it 20 times a day on a single charge? Hard to say, it may at first but as time goes and the battery ages it will lose that ability to hold it's charge because of having to add fluid/water to it during maintenance. All batteries do this as time goes, batteries are by design only meant to last by a certain cycle duty rate, once it gets to that threshold it's ability to retain charge diminishes due to sulfating/contamination of the plates. Every time you have to add water (distilled is preferred) it dilutes the acid and the electrolyte weakens.
I would make sure you have a decent maintenance plan in place to make sure the battery(s), charger and the truck itself is kept in good running condition.
A good average maintenance plan is usually done based on hourly usage, in your case i would have maintenance done at least once a month just because your running up and down that ramp. (maintenance based on hours is generally calculated for normal conditions) which yours is not.
Oh and one other thing, ramps will eat up tires and can be a challenge in adverse weather conditions if it is outside. Keep this in consideration and make sure the operators are well trained before you cut them loose on it. ;o)