PSP Slim (2000) CFW 6.60 PRO B-8 downgrading to 6.20

Tried downgrading to 6.20 from 6.60 Pro B-8 but got stuck at the update screen. (Went to 99%, dropped to 84% in an endless cycle) Now whenever I turn my PSP on it goes straight to the Blue screen after the boot logo. I can't get to the recovery menu, and I know I'm screwed.

Would a Pandora battery fix this? (Please tell me it will)

I need an answer, fast. Thanks.