how to charge battery from another car

[DelSawyer]

To safely jump-start a car battery, you need a set of jumper cables and a second vehicle with a functional battery. The core process involves connecting the cables in the correct sequence to transfer power without causing damage or injury. The most critical rule is to avoid letting the positive and negative clamps touch each other once they are connected to a battery.

You'll need a working car and a standard set of jumper cables. Ensure both vehicles are in "Park" (or "Neutral" for manual transmissions) with the ignition off.

1. Position the Cars: Park the working car close to the disabled car so the cables can reach both batteries, but ensure the vehicles do not touch.
2. Identify Terminals: Locate the positive (+) and negative (-) terminals on both batteries. They are usually marked clearly in red (positive) and black (negative).
3. Connect Positive to Dead Battery: Attach one RED (positive) clamp to the positive terminal of the dead battery.
4. Connect Positive to Good Battery: Attach the other RED (positive) clamp to the positive terminal of the good battery.
5. Connect Negative to Good Battery: Attach one BLACK (negative) clamp to the negative terminal of the good battery.
6. Ground the Last Clamp: This is a crucial safety step. Instead of connecting the final black clamp to the dead battery's negative terminal, attach it to an unpainted metal surface on the disabled car's engine block or chassis. This provides a ground and helps prevent sparking near the battery, which can emit flammable hydrogen gas.
7. Start the Working Car: Start the engine of the working car and let it run for a few minutes to allow its alternator to charge the dead battery.
8. Attempt to Start the Dead Car: Try to start the disabled vehicle. If it starts, leave both cars running.
9. Disconnect in Reverse Order: Carefully remove the cables in the exact reverse order: a) Black clamp from the ground on the jumped car, b) Black clamp from the good battery, c) Red clamp from the good battery, d) Red clamp from the jumped car.
10. Drive the Car: Keep the jumped car running for at least 15-20 minutes to allow its alternator to recharge the battery fully.

Common Jumper Cable Gauge and Capacity
Cable Gauge (AWG)	Recommended Use
6 Gauge	Standard sedans and compact cars; sufficient for most common jump-starts.
4 Gauge	Larger engines like V6 or V8s, SUVs, and light trucks; offers lower resistance.
2 Gauge	Heavy-duty vehicles like diesel trucks; provides maximum power flow.
8 Gauge	Small engines (motorcycles, lawn tractors); not recommended for standard cars.
Typical Boosting Time	2-5 minutes of the donor car running before attempting to start the dead vehicle.

If the car doesn't start after a few tries, the battery may be too old or damaged, or there could be a more significant electrical issue requiring a professional mechanic.

[JoyFitz]

My dad taught me this, and the key is the order. Red to the dead battery's positive first, then red to the good battery's positive. Black to the good battery's negative, and the last black clamp goes on a bare metal bolt in the engine bay of the dead car, NOT on its negative terminal. That last part prevents a dangerous spark. After it starts, let it run a while before you drive off.

[DeMicah]

Safety is the top priority. Always wear safety glasses. Check the dead battery for cracks, leaks, or corrosion before connecting anything. If you see any damage, do not attempt a jump-start; the battery needs replacement. Ensure the jumper cables are untangled and the clamps are not touching. When connecting, be precise to avoid short circuits. A spark near a battery can be extremely hazardous. If you're unsure, it's safer to call for roadside assistance.