How Long Can a Car Battery Last Without Driving?
4 Answers
A car battery can last for about 15 days without driving. Here are the related details: 1. The functions of a car battery are: (1) When starting the engine, the battery supplies power to the starting system, ignition system, and electronic fuel injection system. (2) When the engine is off or idling at low speed, it provides power to the car's electrical equipment. (3) When the alternator's output is insufficient, it can assist in supplying power to the electrical equipment. (4) It mitigates voltage surges in the electrical system, protecting the car's electronic devices. (5) It stores excess electricity generated by the alternator. 2. Battery maintenance methods include: (1) Starting the car periodically to recharge the battery. (2) Adding distilled water or a special replenishing fluid when the electrolyte level is low. (3) Regularly checking the ventilation holes on the battery cover and inspecting the positive and negative terminals for signs of oxidation during daily driving.
Last time I came back from a one-month business trip and found my car wouldn't start. The 4S shop technician said the battery was completely drained. Actually, car batteries slowly discharge just like phones in standby mode. A new car might be fine sitting for 2-3 months, but an older vehicle could drain in just 2-3 weeks. My neighbor's five-year-old American car completely died after sitting for three weeks during the pandemic. The key factor is how many 'power vampires' your car has - dashcams can secretly consume 0.5 kWh/day, and the anti-theft system also draws power. For long-term parking, it's recommended to start the engine every half month for 20 minutes to recharge, or disconnect the negative terminal. Once I tried connecting solar panels to the battery, and it stayed strong for three months.
After testing the data from over a dozen idle company vehicles, we found that battery lifespan mainly depends on three factors: capacity (a 60Ah battery lasts longer than a 45Ah one), age (a battery within three years can still retain about 80% of its charge), and the number of additional devices installed. In our fleet, a GL8 equipped with two sets of ambient lights dropped below 10V in just two weeks. Under normal conditions, the voltage decreases by about 0.1V per day, and the car won't start if it falls below 11.8V. If long-term parking is unavoidable, connecting to a smart charger is the most reliable solution, as such devices automatically cut off power to protect the battery.
The most extreme case seen in a repair shop: a BMW with start-stop function was completely drained after just ten days of parking. These batteries are particularly delicate. While a regular car battery might still start after three months of inactivity, an AGM battery (used in start-stop systems) is usually dead after over a month. It's recommended to check the voltage with a multimeter before business trips. If it's above 12.4V, it might last a month; if below 12V, it's best to disconnect the negative terminal. For vehicles with 24-hour monitoring devices installed, connecting to an external power source is the safer option.
