If the battery replacement doesn’t solve the misfire code — may take some drive cycles for it to disappear — they way to diagnose misfires is to swap stuff between cylinders. For example if you swapped the spark plugs between cylinder 6 and 5, and the misfire moved from 6 to 5, excellent chance the problem is a faulty spark plug. Coils, injectors, wiring, etc are all possibilities for swapping. Misfires can also be caused by low cylinder compression.
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