The man said it Always connect the positive + cable first to the battery. Then connect the negative- cable to the engine somewhere. Never connect the negative cable to the battery itself. Batteries vent hydrogen gas and which can ignite with the slightest spark. For this reason never, ever, connect the negative first and never connect the negative to the battery.
The negative battery lead cable is to be connected to the negative lead terminal on the battery.
Connect the Positive + battery cable to the positive + battery post first. Then connect the Negative - cable to the negative - battery post.
If you connect a negative battery terminal to another negative terminal, you would be creating a short circuit, which can lead to excessive current flow and potential damage to the battery or the connected devices. It is not a recommended practice and can be dangerous.
Negative battery or jump start post.
Connect the positive + red charger cable to the positive + red battery post. Then connect the negative - black charger cable to the engine somewhere. Most engines have something metal sticking up that you can connect to. Do not connect the negative charge cable to the negative battery post, always connect it to the engine.
Connect the negative cable first.
First off you must have the same type batteries. Connect the positive post of the first battery to the positive post of the second battery. Then connect the negative post of the first battery to the negative post of the second battery. Now connect the positive post of the first battery to the positive connection on the vehicle. Then connect the negative post of the first battery to the negative cable of the vehicle. Click the link for a diagram.
At the battery if at all possible.
Connect a battery charger to battery positive to positive negative to negative
Connect them together in Series. Connect the negative post of one battery to the positive post of the other battery. Then connect the negative charger cable to one negative battery post and the positive to the positive post of the other battery.
Connect positive to positive post (red) on the battery and connect the negative to a place on the engine away from the battery.