As for the latest technology - yes, there have been improvements since diesel-electric hybrids started being sold, but the basic layout has stayed the same. See for instance this 2009 piece about Yosemite's new (at the time) hybrid shuttle buses.

[www.edmunds.com]

The buses are still in service, but the park is having difficulties because the traffic is so clogged that the buses can't maintain any kind of schedule. Plus, of course, riding city buses to get around Yosemite Valley (some of their old diesels had windows in the roof like the old Gray Line buses in SF, but not these)? Though what the options are, other than driving a car, riding a bike or horse, or walking, I don't know; when I go, if I'm going to stay a few nights, I usually throw the bike in the back of the car and use it for running around the Valley.

BTW, modern hybrid vehicles (car and bus) usually use AC motors, not DC. Voltage depends on the battery system used but is seldom more than 400-500V. Seattle had some dual-power diesel-electric buses at one time - diesel on the street, trolley in the downtown tunnel that's now for light rail - but that was much older tech and was not "hybrid" with a traction power battery.