I seriously doubt that upgrading to Diablo via unsupported and hackful SSU from Chinook will have any difference in battery life.

For my (anecdotal) evidence:
I used:

• Chinook on internal flash: Good battery life.
• another Chinook on the SD: Good battery life.
• pseuDiablo on the SD: Good battery life.
  (There was not, among these 3, any discernable difference in ordinary usage; I didn't do any actual tests with reproducible load, though.)
• Debian on the SD: I never used it long enough without rebooting to draw any conclusions.

Now I've got:

• Diablo (released) on internal flash: Good battery life.
• Chinook on the SD (clone of the previous Chinook/internal): Good battery life.

I don't see any substantial difference, and there's no reason there should be. However, almost all of these installations occasionally had severe battery drain, when I accidentally left some process stomping at 100% CPU; metalayer-crawler (until I disabled it on each installation, of course) and the browser were the most frequent offenders.