I have a psp 1003 (A.K.A Phat), I am on FW 6.20 TN-E. I want to downgrade to FW 5.50 GEN-D (full)

I am able to downgrade to 5.02 OFW or higher useing the version.txt(5.00) then install a FW higher than 5.00, i install OFW 5.03 then try to install ChikenR2 but i never can i've tryed to for hours and days on end, i know that the files are all in the right place because i've watched over 20 tutorials on how to do that, so i was wondering in somebody could give me corect details for a version.txt thats maybe around FW 3.00 or as close as possible so i can install a lower CFW then upgrade to 5.50 GEN, as i have already try editing it to FW 2.00 and many others, it works and shows up in the settings as those FW but i try to update to a OFW thats a little bit higher it starts and opens then usealy it comes up with the menu thingy but mine say 'The update cannot be started. the data is corrupted.'
PANDORA WAY - I have also try hard-moding both of my psp batterys but none of them have the ICO-4 chip (i think its that chip, i know for certain that it has 4 pins ethier side though, but no chips have 4 pins on my 2 batterys) i've tryed soft-moding them too, but it says 'unable to write to the battery EEPROM'

So please if any one could help, it would be most greatly thanked.
Thankyou so very much.