Why Cars Lose Battery Charge During Storage
Even with the engine off, your car's electronic systems keep drawing power. The ECU, alarm, keyless entry, and clock all consume small amounts of current around the clock. This parasitic drain slowly depletes the battery. In cold or hot weather, battery efficiency drops further, accelerating the discharge rate and potentially leaving you unable to start the car.
How the Calculation Works
Daily drain (Ah) = total current (mA) × 24 hours ÷ 1,000. A 50% safety margin prevents deep discharge damage. Temperature efficiency adjustments apply for extreme outdoor conditions. The result is the estimated number of days before the battery reaches the deep discharge threshold.
Frequently Asked Questions
Sometimes, but not always. Batteries discharged below 10V often have sulfated plates that prevent normal charging. If the voltage has dropped that low, replacement is usually the better option.
Yes. A dashcam in parking mode typically adds 50–100mA, which can cut storage time in half. Turning it off or setting a voltage cutoff is strongly recommended for storage longer than two weeks.