Originally Posted by DHC8-FO
You dont have to unfeather the first one prior to starting the second one.
Our manual stated to keep them both in feather until the tow bar and/or external power is disconnected.
I think you misunderstood the question. He specifically asked about internal start, ie battery start (no APU, no Ext power).
The Flight Manual states:
"When battery starting, unfeather propellor of first engine and delay start of second engine for 30 secs to allow completion of flight guidance computer start-up self-test."
In our company, we do battery starts with the bus feed CB's pulled, bus tie off and inverters off. After starting #2, unfeather and then reset CB's, inverters on and tie buses.
When the prop is unfeathered, the AC gen comes online. I can only imagine that that is the reason, to make an extra generator available. With APU starts, you have the APU gennie helping and with external you don't need generated power (in fact DC gennies are isolated while external power selected).
Hope this helps Capt Grease-on.