It's a 23,000 watt hour rated lead-acid battery that has been "out of service" for 4 years. As a 48V setup it reads 50.5V on the person's meter.
My understanding is that 12V-rated SLA batteries are at 13V when charged so that person's pack is substantially below that (or being measured inaccurately).
I think if a pack will actually only charge up to 97% of its rated voltage, it might provide a LOT less than 97% of its rated watt hours.