can you charge car battery from another battery

[McPhoebe]

Yes, you can charge a car battery from another battery, a process commonly known as jump-starting. However, it's crucial to understand that you are not slowly recharging the dead battery but rather using the good battery to provide a burst of power to start the engine. Once the engine is running, the car's alternator takes over to recharge the battery. For a true, slow recharge using another battery, you would need a separate device like a portable jump starter or a battery charger.

The most common method is a jump-start with jumper cables and a second vehicle. The key is correct connection to avoid dangerous sparks or damage to the vehicles' electrical systems. Always connect positive to positive (+) and negative to negative (-), with the final negative clamp attached to an unpainted metal surface on the dead car's engine block, not the dead battery itself.

For a safer, more controlled charge without a second vehicle, a portable jump starter or a dedicated battery charger is a better investment. These devices are designed for this specific purpose and eliminate the risks associated with a traditional jump-start.

Method	Primary Function	Risk Level	Best For	Key Consideration
Jumper Cables (2nd Car)	Engine Start (Alternator recharges)	Moderate	Emergency roadside situations	Requires a donor vehicle and knowledge of correct connection order.
Portable Jump Starter	Engine Start (Alternator recharges)	Low	Solo drivers, frequent short trips	Must be kept charged itself; compact and convenient.
12V Battery Charger	Slow, Full Recharge	Very Low	Reviving a drained battery at home	Takes several hours; the only method that truly "charges" the battery.
Deep Cycle Marine Battery	Slow, Full Recharge (with charger)	Low	Off-grid scenarios, long-term storage	Requires a separate 12V battery charger to connect the two batteries.

After a successful jump-start, you should drive the vehicle for at least 20-30 minutes to allow the alternator to sufficiently recharge the battery. If the battery dies again soon after, it likely indicates an old battery that can no longer hold a charge or a problem with the alternator.

[VonColeman]

Yeah, you can do it, but be careful. I've had to jump my old truck more times than I can count. The main thing is connecting the cables right. Red clip on the dead battery's positive terminal, then the other red clip on the good battery's positive. Black clip on the good battery's negative, then the last black clip on a bare metal bolt in the dead car's engine bay—not on the dead battery. Messing up the order can cause sparks or worse. Once it's running, let it idle for a while so the alternator can put some charge back in.

[SanTravis]

My main concern is safety. Connecting two batteries incorrectly can cause a spark near battery gases, which may lead to an explosion. It can also fry your car's expensive computer system. If you're not 100% confident, calling for roadside assistance is the safest bet. If you proceed, wear safety glasses. The correct sequence is vital: positive to positive, then negative from the good battery to a ground on the dead car. Disconnect in the reverse order once the car is running.

[LaAmara]

Think of it as a temporary boost, not a full charge. The goal is just to get the engine started so the car's own alternator can do the real charging work. For a proper, slow charge without the engine running, you'd need a different tool. A portable lithium jump starter pack is a fantastic modern solution. It's like a big power bank for your car—no second vehicle needed. They're relatively inexpensive and much safer than dealing with messy cables, especially if you're not mechanically inclined.

[DiJace]

Technically, a direct battery-to-battery connection for a slow trickle charge is possible but impractical without the right equipment. You can't just run wires between them. You need a device like a 12-volt battery charger to manage the voltage and current flow. Alternatively, a DC-to-DC charger is used in RVs for this purpose. For the average person, the "jump-start" is the relevant procedure. It works because the good battery acts as a surrogate, providing the massive amperage (cold cranking amps) required to turn the starter motor, which the dead battery cannot do alone.