A search yielded the voltage is regulated by the computer.
Still curious what the voltage is.
Decided to go with the Deka ETX30L.
Apparently there is some concern that the lithium doesn't have a smart charger built in, so there is a chance to damage it if overcharged (over 14.4 volts, or over 10 amps). Or if the cells do not charge equally, one could lag, causing the others to overcharge (each cell is 3.6v x 4 cells). Best explained on post #17 here:
Lucky Man's Lightweight Battery - Pelican Parts Technical BBS