The alternator isn't working right.
An alternator can malfunction in a lot of ways. It can provide too much or too little voltage, not enough current, no current or the wrong kind of current. The wrong kind would be AC voltage instead of DC. Once several basic checks are done, replacing the alternator is justified. It needs a “turn on” command from the computer. The belt and the battery wire connected to it needs to be checked. A qualified mechanic from YourMechanic can come out and diagnose your battery and alternator if you need further assistance.
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