can you charge a battery off another car

[VonJames]

Yes, you can charge a car battery using another vehicle, a process commonly known as a jump-start. It's a reliable method to get your engine running again when the battery is dead, typically due to leaving lights on or in cold weather. The core principle involves using jumper cables to connect the dead battery to the good battery in another car, allowing the second vehicle's alternator to supply the necessary power to start the first.

Safety is the absolute priority. A mistake can lead to battery explosion, electrical system damage, or serious injury. Before you begin, ensure both cars are in "Park" (or "Neutral" for manual) with the ignitions off. Engage the parking brakes. Inspect both batteries for any cracks, leaks, or corrosion. If you see damage, do not proceed.

You will need a set of jumper cables with thick wires and sturdy clamps. The correct connection sequence is critical:

1. Red Clamp (+) to Dead Battery: Connect one red clamp to the positive terminal of the dead battery.
2. Red Clamp (+) to Good Battery: Connect the other red clamp to the positive terminal of the good, donor battery.
3. Black Clamp (-) to Good Battery: Connect one black clamp to the negative terminal of the good battery.
4. Black Clamp (-) to Engine Block: Connect the final black clamp to an unpainted, metallic part of the dead car's engine block or chassis. This provides a safe ground, away from the battery itself, to minimize the risk of sparking near battery gases.

Start the donor car and let it run for a few minutes. Then, attempt to start the car with the dead battery. If it starts, carefully disconnect the cables in the reverse order. Drive the jumped car for at least 20-30 minutes to allow its alternator to recharge the battery. If the car dies again soon after, the issue may be a failing alternator, not just the battery.

Factor	Consideration & Data
Typical Cause of Dead Battery	Parasitic drain (e.g., interior light left on), extreme temperatures, old age (batteries last 3-5 years on average).
Time to Transfer Charge	Let the donor car run for 5-10 minutes before attempting to start the dead car.
Jumper Cable Gauge	A lower gauge number is better. Use 4-gauge or 6-gauge cables for sufficient power flow; avoid thin 10-gauge cables.
Battery Voltage	Standard car batteries are 12 volts. Connecting a 12V to a 12V system is safe.
Modern Vehicle Considerations	Many new cars have sensitive electronics. Using a portable jump starter pack is often a safer alternative to avoid voltage spikes.

[EmilioFitz]

Been there, done that. Yeah, you can definitely jump a car from another one—it’s a lifesaver. The key is doing it safely so you don't fry anything. Red clamp goes on the dead battery's positive terminal first. Then the other red on the good battery's positive. Black on the good battery's negative, and the last black on a bare metal spot on the dead car's engine. Start the working car, wait a minute, then try starting the dead one. Just be super careful not to let the clamps touch.

[StTheo]

Absolutely, this is a standard procedure. It's crucial to understand that you are not "charging" the dead battery in the traditional sense over hours. You are providing a high-amperage boost to crank the starter motor. Once the engine is running, the car's own alternator takes over to recharge the battery. For modern vehicles with complex computer systems, a sudden voltage spike from a poor connection can cause damage. A modern portable lithium-ion jump starter is often a safer, more controlled solution that doesn't require a second vehicle.