How can car battery change affect subaru?

In what aspect? You haven't given enough information about the problem to answer.How can car battery change affect subaru?A new fully charged 12 volt battery should test with a volt meter 12.85 volts. After it's installed in the car with the motor running the battery terminals should read between 13.5 -14.2 volts. That's assuming the alternator and internal voltage regulator is up to snuff.
How can car battery change affect subaru?
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How can car battery change affect subaru?
If it is affecting your Subaru, you will need to state what the effects are.
Having a charged battery will allow the vehicle to start. Once it's started, it can run off the alternator.