A car battery draining overnight usually results from a parasitic drain, which occurs when an electrical component continues to draw power even when the car is off. Common culprits include interior lights, faulty alarms, radio memory, or malfunctioning relays.
Another possible cause is extreme temperatures affecting battery efficiency. Cold weather slows chemical reactions, making it harder to retain charge, while hot temperatures cause fluid evaporation. A weak or aging battery is also more prone to losing charge quickly.
To diagnose the issue, check if any lights or electronic devices remain on after turning off the car. Using a multimeter to test for voltage drops can help identify excessive power draw. If your battery continues to drain despite troubleshooting, replacing it with a new Car Battery may be the best solution.