Battery dying when car not in use. Can it be my alternator?
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The clamp on my positive battery recently cracked and the car would not start. Brought it to the shop and they replaced the clamp with a clamp from a Mazda because they said only other option would be to buy a $600 harness from Hyundai. Also put in new battery. This was 3 months ago. Now (last few weeks ) battery light on dashboard lights up. I suspected the alternator is failing. I haven’t touched the car in a week and now battery is completely dead. I charged the battery and while running I used my multimeter and see 11.5. - 12. 5 volts so not charging. Let sit a few more days and battery is dead. So the question is, can the battery die while sitting in my driveway, car not turned on, fully charged battery if only the alternator is bad. I suspect something else is draining the battery but just want to rule out the alternator. Hope someone can help. Thanks
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Hi, this is Bo, an auto expert on RepairPal's Car Genius team!
It sounds like you're dealing with a couple of issues here. Based on the voltage readings you took, it does seem like your alternator isn’t charging the battery properly. When the engine is running, you should see around 13.5 to 14.5 volts if the alternator is working correctly. Since you’re only seeing 11.5 to 12.5 volts, your alternator likely needs replacement or repair.
Now, as for your battery dying while the car is sitting, that points to a parasitic draw—something in your car is draining power even when it’s off. The alternator itself usually doesn’t drain the battery while the car is off, but if there's a short or issue within the alternator, it could potentially cause a drain. You might want to check for any other accessories, lights, or modules that could be drawing power while the car is off.
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