* Bad Battery (despite being new): While unlikely, a faulty new battery is possible. It could have a manufacturing defect or been damaged during installation. Get it tested at an auto parts store to rule this out.
* Alternator: This is the most likely culprit. The alternator recharges the battery while the engine is running. If it's failing, it won't recharge the battery, and eventually, the battery will drain completely, even a new one. A failing alternator often shows symptoms like dim headlights or other electrical issues before complete failure.
* Faulty Wiring/Corrosion: Look for loose, corroded, or damaged wiring, particularly around the battery terminals, alternator connections, and the starter. Corrosion can create high resistance, preventing proper charging and starting. Clean all connections thoroughly.
* Parasitic Drain: Something in your car's electrical system might be drawing power even when the car is off. This could be a malfunctioning component (like a radio, dome light, or a faulty alarm system) or a short circuit somewhere in the wiring. This is harder to diagnose and may require a professional mechanic.
* Starter Motor: While less likely to cause a complete electrical outage, a failing starter motor could draw excessive current, draining the battery quickly.
* Body Control Module (BCM) Issues: The BCM controls many electrical functions. A problem with the BCM could cause a sudden power loss.
Troubleshooting Steps:
1. Test the Battery: Have the battery tested at an auto parts store. This will determine its voltage and cranking amps, revealing if it's truly the problem.
2. Check the Alternator: With the engine running, have the alternator tested (again, at an auto parts store). This checks its output voltage.
3. Inspect Wiring and Connections: Carefully examine all wiring and connections related to the battery and alternator, looking for corrosion, looseness, or damage. Clean any corroded terminals with a wire brush and baking soda solution.
4. Check for Parasitic Drain (Advanced): This requires a multimeter to measure the current draw when the car is off. If there's a significant drain (more than 50 milliamps), it points to a component drawing power constantly. This is best left to a mechanic.
If you're not comfortable performing these checks yourself, take your car to a trusted mechanic or auto repair shop. They have the tools and expertise to diagnose the problem accurately. Don't attempt major electrical repairs yourself unless you have significant experience.
