As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING HEAVY MAINTENANCE, INOP EPSU BATTERIES AT 13WL AND 15WL; (REF AE NR 2020-42502, W/O 2020-16/1) PERFORMED TSM 33-51-00-810-879-A(13WL) AND 33-51-00-810-875-A(15WL). BATTERIES REQUIRE REPLACEMENT. REPLACED BATTERIES IAW AMM 33-51-38-400-002-A. OPS CK'D IAW AMM 33-51-00-710-001-A TESTS OK.