The steps i would take in this case are thes:
Step 1. Send it to sony for repair, tell them in the form that it broke down because of a battery malfunction while updating with OFW. If that doesen't work go to step 2.
Step 2. Try to get a friends older mobo or something like that, screw it in and see if it works with the chipset or if it malfunctions, If it works go to step 3 if it doesen't go to step 4.
Step 3. Buy the same Mobo your friends or whoever you tricked into lending him his/her mobo and buy the exeact same type and tada your done, skip to step 5.
Step 4. Buy a original TA88V3 board screw it in and go to step 6.
Step 5. Tada your done, now you can flash it with a CFW if it is a older version Mobo with OFW 5.03 or lower, Go to the final step.
Step 6. Tada your done, you can if you want now flash it with chickHEN D2 IF the mobo boxcode is D or lower Go to the final step.
Final step: Do not throw away your old mobo there might be a fix in the future because there are alot of ppl that fcked up there psp this way, if a fix comes out, fix it and or use it or sell it for some $
That's what i would do