Captain Sim wrote on Apr 25^th, 2012 at 12:00am:

Markoz wrote on Apr 24th, 2012 at 4:01pm: I was using the 737-200 and I was not using the APU or External Power/Bleed Air. After a while, the power went out. The battery had died. 1. Does this happens every flight? 2. Are you sure the generators are ON? 3. What happens if you ARE using the the APU or External Power for the startup?

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1. NO
2. Yes NO - I was confusing the Engine Bleed Air valves with the Generators.
3. They were not in use when the power was lost. I can't start the APU or turn on EP/BA once the power is lost. I used CTRL+E to start the engines, but I could not turn the generator switches ON to get any power to the aircraft.

This does not happen every flight. It has only happened to me twice so far. I can't "nail" what exactly causes it. Both times I noticed that the landing gear had disappeared (they are the only times the landing gears disappears on me).
Last night, after it happened and I restart FSX, the 737-200 sat at the Gate for 2 hours using only the battery for power (the APU was OFF and EP/BA was OFF) and it still had power. So it has me bamboozled.

This is what I normally do once the 737 is loaded into FSX:

Battery Switch - ON (and then close the Battery Switch Cover)
Simicons Panel - EP/BA - ON
Ground Power Switch - ON
Yaw Damper Switch - ON
Fuel Pump Switches - ON (if no fuel in Center Tank its pumps remain in the OFF position)
DC Meter Selector - BAT
AC Meter Selector - GRD PWR
Galley Switch - ON
No Smoking and Fasten Seatbelt Switches - ON
Window Heat Switches - ON
Pitot Static Switches - ON
Gasper Fan - ON
Left and Right Air Conditioning Packs - ON
Isolation Valve - OPEN
Engine Bleed Air Switches - ON
Position Light Switch - ON

The only difference was that when it last happened, I did not use EP/BA, and so the switches on the Air Conditioning panel, may not have been on (I normally turn them on after I turn on the EP/BA or APU). When 737 lost the power, all the switches were turned OFF except the Battery Switch. The Battery Switch Cover was closed and unable to be opened to gain access to the Battery Switch (seeing as the cover can only be closed when the Battery Switch is ON, I assume that it IS still ON).

@bud7h7 - The engines were OFF when the power was lost. I was NOT using any other source for power except the Battery Switch being ON.

Mark