boot up problem (battery/raid)?

hi all,

machine:

Jan 2008 mac pro w/ Apple raid card, 4 x 500 GB Wetsren Digital enterprise drives & 16GB RAM form OWC

problem:

i made two raid 0 arrays and put my boot partition on the first one (btw i know it's risky but i have an external
esata drive for boot partition mirroring). then every morning, after having unplugged everything over night, i
started getting the blinking question mark. the funny thing is, when i turn the computer back on a few seconds later
it boots just fine every time, and if i reboot during the day it also works just fine.

so i figured even though boot off raid is meant to be supported, that it was flaky, so i put boot on a single jbod,
and made a 3 disk raid 0 array for users. this worked fine for about a week but the exact same symptoms are now
manifesting. apple hardware test passes (although i haven't run the extended one, but that just tests RAM right?).

my guesses in order of likelihood:

bad pram battery
bad raid card battery
logic board / battery interface busted
bad hard drive(s)
screwy raid card

any enlightened commentary/advice or even wild goose chase guesses very much appreciated.

thanks,
_c