My 2008 Honda Civic has been having issues where the battery keeps getting overcharged. The voltmeter reads about 15.5 volts at idle, which seems way too high. The battery terminals get warm and I'm worried it'll damage the battery or electrical system. What's the best way to test if it's actually the alternator causing this?
At 15.5 volts you're definitely into overcharge territory - a healthy alternator should sit around 13.5 to 14.5 volts. The first thing to do is disconnect the negative battery terminal with the engine running and see if the voltage drops back to normal; if it does, the alternator's voltage regulator has failed and you need a replacement. If the voltage stays high, it's likely an internal short in the regulator or a stuck field circuit, which again means replacing the alternator. Warm battery terminals confirm the system's been pushing too much current, so get this sorted soon before you cook your battery or damage other electronics - on a 2008 Civic this is usually a straightforward swap of the alternator unit itself.
Log into answer.
