... I have needed to jump start the bus. Since I did not have a 24v supply, I used the 12v house bank with jumper cables to one of the start batteries. Therefore, really just jumping one half of the 24v system. It has worked several times. ...
Lin, I have no info on your idea of a solenoid-switch crossover, but my bus is parked at a charter bus operations lot. The buses have high watt entertainment and lighting systems and the drivers (most of whom are part-time school bus drivers) as forever forgetting to turn off the bus master switches. Man, that business goes through 8-D's like Sherman went through Georgia. But when they catch the situation when the batteries are just down and not totally killed, they put a 12V jump box on one battery. In almost all cases, that starts the buses right up.
So, I'm thinking that one good, high-capacity jump box (kept fully charged, of course) would probably do us for most of our practical low start battery conditions. If someone were to be really concerned, you could have a pair of jump boxes.
And the way I have it set up, I could always put one of the jump boxes on the 12V battery for my generator, get the generator going, and put the battery chargers on the start batteries. When the chargers read "Floating" on the digital readout, my bus always starts easily right down to freezing. But I don't know if you have a separate battery for starting your gennie.
But, as to your question of boosting just one battery, yeah, that seems to work fine under most conditions. But, I'd also be thinking about those critical conditions where I needed to add juice to both batteries. BH NC USA
(PS - The buses I've seen involved in this are -- 1] Cummins - M11; 3-4] 8v-Something DD 2-smokes's; 1] International DT-455 (or something like that). Works on all of them.)