I haven't tried cutting power to my 990, so I can't say for certain how long it'll go without forgetting. Outlaw may have some good info for you, though - you can call or
contact them online . My old Model 950 was based on a different platform and came from a different factory than the 990, but it came through a
windstorm-induced outage with its memory intact - that makes me suspect it was using non-volatile memory that should go for a
very long time without forgetting. If the 990 uses similar memory to store its settings, it should yield comparable results.