[unwind]

This part makes it even more confusing:

In the battery compartment, nine trays were used to hold a 500 pound, five-foot-long lead-acid battery pack that produced 10 volts.

I guess it is 10 volts per cell, not for the entire pack? With 9 cells in series that would give 90 V which sounds close enough.

Still confused. :)

[Dylan16807]

The missing word is "each", I believe. 9 packs, 10V per pack, each pack (consisting of 5 batteries) weighing 500lb.

[vsizov]

Yeah, I was also confused by 2 hours charge. It's very uncommon for lead-acid batteries...