By removing the negative cable first, you remove the chance for the positive terminal to throw that spark, or arc, because the battery is no longer grounded to the car.
Negative first
It's important to disconnect the negative side of the battery first, otherwise you can cause an electrical short if the positive is removed first.
Make sure you disconnect the negative terminal first. Lay the disconnected negative cable carefully to one side, making sure it's well away from the battery terminal.
Once disconnected the positive will not pose a short risk to the frame either. If you disconnect the positive terminal first, one slip of your wrench could send a direct short to the ground, which can be very dangerous.
Tip #1: Never connect the black cable to the negative (–) terminal on your dead battery. This is very dangerous, as it could result in an explosion.
Connecting the negative terminal first can create a short circuit, potentially damaging the battery, and electrical system, or even causing injury. By connecting the positive terminal first and then the negative, you can minimize the risk of any accidents or damage, ensuring a safe and successful installation.
Connecting the battery terminals in reverse can cause serious damage to the battery itself, the electrical components, and even to yourself. Each terminal of a car battery uses 12V of current with positive and negative orientation.
When disconnecting the cables from the old battery, disconnect the negative first, then the positive. Connect the new battery in the reverse order, positive then negative.” When you are replacing your car battery, It isn't always easy to remember the order in which to disconnect and reconnect the terminals.
Disconnecting the negative (chassis lead) will protect the electrical side of the battery. Removing the battery and storing it inside will protect the physical battery.
Will the Car Battery Drain if the Negative Cable Is Disconnected? A car battery will self-discharge at a rate of 5-15% per month with the negative terminal disconnected. However, the alternative option of leaving the battery connected while it isn't being used will drain at close to 20% per week.
Remember: in a battery, electricity flows from the negative end to the positive end. If the positive and negative ends of a battery come into direct contact with each other, a short circuit occurs. Result: the battery will drain very quickly. Very rarely, a sudden release of energy can cause a sudden burst of heat.
Simple reason. The entire body of the car along with the engine is connected to the negative terminal of the battery. If you're disconnecting the positive terminal first, and the spanner touches any part of body or engine, you'll get a massive spark and potentially damage your battery also.
Removal of Old Battery
Remove the negative (-) terminal first. This precaution is necessary to avoid damage to wiring and the battery by accidentally grounding tools. Remove the positive (+) terminal.
Negative terminal: The battery terminal that facilitates current flow via an external circuit to the positive terminal during discharge.
Important: The cable which is connected to the negative terminal must be disconnected first. This prevents a short circuit between the positive terminal and ground. Then disconnect the red cable which is connected to the positive terminal.
Disconnect your battery terminals before leaving – this prevents your battery from losing charge. Remember, you just need to disconnect the negative terminal.
A Final Note: If you're removing the battery cables to store your ride for an extended time, know that a fully charged battery will hold its charge for six months to a year if you disconnect the negative cable.
Yes, a car will stay running if you disconnect the battery. This is because the alternator should provide sufficient energy to power the vehicle even when the battery is removed. However, if the vehicle dies, you have a faulty alternator that should be replaced.
Connect positive first, negative having less potential won't arc. The higher the voltage, the greater the chance of arcing and fusion.
If you connect the negative first, then if your wrench brushes the chassis while tightening the positive, you could get a large spark. If you connect the positive first, you slipped wrench does not close a circuit.
If the engine's already running, disconnecting the battery will still keep the engine running. If you're trying to start a car without a battery or with a very dead battery, it won't start (even with push start in a manual car) because there's no electrical supply (spark) to the combustion chamber.
The alternator's design makes it fairly impervious to negative effects from jump starting. However, the alternator can sustain instant damage if the polarity of the clamp connections is mistakenly reversed.
The reason for connecting the negative cable to ground rather than to the negative terminal of the dead battery is to minimize the chances of a spark near the battery, where there may be potentially explosive gasses.
Tom: The danger from car batteries is not so much electrocution as it is explosion. If you touch both terminals with a metal wrench, for instance, you can create a spark that can ignite hydrogen gas in the battery. That can send pieces of battery and acid flying.