Start with How to Replace the Oil in a Tesla (14 min, ChrisFix), then How to Replace a Hybrid Battery in a Prius (Upgraded Battery) (40 min, ChrisFix). All 166 lessons here are free, from the teachers' own official uploads. You'll need insulated tool set (1000 v), class 0 electrical gloves, obd2 scanner (about $210 of kit). The book to keep beside you: Build Your Own Electric Vehicle by Seth Leitman.