Missing battery

[transit360]

I have two matching '98 Bluebird QBRE shuttle buses. One bus has
two 8D batteries. The other only has one 8D battery. Why I don't
know..I just bought them this way a few months ago.
The bus with one 8D battery recently has shown symptoms of a
voltage regulator going out, which includes the voltage spiking
randomly to 16 and 18 volts. Sometimes I can help tame this by turning
on all my fans and A/C equipment so the spike it not so high. It just
shows up randomly here and there while I'm driving. Do you all think
it's the regulator as well?
I was wondering if only having the one battery may have caused
damage. Would it? I've read other sites stating the alternator only
puts out as much as what is drawn by the vehicle. What if the bus were
running at nightime with the lights on, the A/C on and a few other
electrical draws? Would it hurt the battery to transfer the power
necessary to power all these things? Or does it matter?

Steve
2 '98 QBRE Partybuses