With just the batteries on you have the Main buses as well as the essential buses powered. After you start the first engine you have the and leave it in feather you still only have the mains and essentials powered.(The difference is 28 volts from the DC GEN instead of 24 volts from the bat)
Bringing the propeller out of feather now activates the AC GEN for that engine. It will now power the secondary buses via the TRUs. The DC GEN is still powering mains and the essentials. You now have the whole dc system available, however the load on the DC GEN has not changed because it is still powering the same buses it was before you unfeathered the propeller.
Off to sim today I'll see u guys in a couple of days.