A car battery provides the electrical energy needed to start the engine and power all the various electronic devices when the car is not in motion. Although a car battery is normally charged by the alternator when the car is in motion, it may happen that the battery is flat and needs to be connected to a charger. Like when you start a stationary car by connecting its battery to another car through terminals, to connect a dead battery to a charger you will have to be careful what you do to avoid damaging the battery or hurting yourself.
Steps
Part 1 of 3: Before Connecting the Charger
Step 1. Familiarize yourself with the characteristics of the battery and charger
Read the manual of the charger, of the battery, if any, and that of the vehicle in which the battery is installed.
Step 2. Choose a well-ventilated work area
Working in a well-ventilated area will help disperse the hydrogen gas that batteries generate due to the sulfuric acid used as the electrolyte in their cells. The fact that hydrogen is volatile means that the battery can explode.
For this reason, always wear safety glasses when recharging a battery. Also, be sure to always keep any other volatile substances such as gasoline, flammable substances, or things that could trigger an explosion (open flames, cigarettes, matches, lighters) away from the battery
Step 3. Determine which battery terminal is connected to vehicle ground
The grounded terminal will be the one connected to the vehicle chassis. In most vehicles, the grounded one is the negative terminal. You can recognize the battery terminals in several ways:
- Look for signs like “POS”, “P”, or “+” on the battery case to find the positive terminal and “NEG”, “N”, or “-“to find the negative one.
- Compare the diameters of the terminals. In most batteries, the positive terminal is thicker than the negative one.
- If the car wires are still connected to the battery terminals, look at their color. The wire connected to the positive terminal should be red, while the one connected to the negative terminal should be black. (It is an opposite color system to that used to indicate income (positive) and expenditure (negative) in financial reporting)
Step 4. Find out whether or not you will need to remove the battery from the car in order to recharge it
This is information you should be able to find in the vehicle manual.
If the battery to be recharged belongs to a boat, you must remove it from its housing and charge it on land, unless you have a charger specifically designed to charge the battery without removing it from the boat
Part 2 of 3: Connect the Charger
Step 1. Turn off all electronic devices in the vehicle
Step 2. Disconnect the cables from the battery
Before removing the battery, first disconnect the grounded terminal, then the other.
Step 3. If necessary, remove the battery from the vehicle
It is advisable to use a battery case to transport the battery from the vehicle to the place where the charger is located. In this way, you will avoid putting pressure on the walls of the battery causing acid to leak out of the upper caps, as it could happen if you were carrying it by holding it in your hand
Step 4. Clean the battery terminals
Use a mixture of baking soda and water to remove any traces of corrosion and sulfuric acid (which will be neutralized) from the terminals. You can apply the mixture using an old toothbrush.
- You can also remove any traces of corrosion from the terminals by using a special round metal brush, which is applied around the terminal and rotated to clean it. These toothbrushes are available from any auto parts.
- Do not touch your eyes, nose or mouth immediately after cleaning the terminals of a battery. Do not touch the whitish deposits that you may find near the battery terminals, it is sulfuric acid.
Step 5. Pour distilled water into each of the battery cells until they reach the optimum level
This will allow the battery to release hydrogen. Follow this step unless the battery in question is one that does not require any type of maintenance, in which case just follow the instructions given by the manufacturer.
- After filling them, replace the caps that seal the cells. Most batteries are equipped with a flame arrestor. If your battery does not have flame arrestor caps, place a wet cloth over the cell opening.
- If your battery caps are not removable, do not touch them.
Step 6. Place the charger as far away from the battery as possible, as far as the cables allow
This will reduce the risk of sulfuric acid vapors damaging the charger.
Never place the battery on the charger or vice versa
Step 7. Adjust the charger output voltage selector to charge the battery to the correct voltage
If the correct voltage is not printed on the battery itself, you should be able to find it in the manual of the vehicle the battery was installed on.
If the charger you are using allows you to adjust the charging speed, initially set it to minimum
Step 8. Connect the charger contacts to the battery
First connect the terminal of the charger to the battery terminal not connected to ground (usually it will be the positive one). The other terminal will need to be connected to the grounded terminal, depending on whether the battery has been removed from the vehicle or not.
- If the battery has been removed from the vehicle, you will need to connect a clamp or insulated wire at least 60cm long to the terminal that should be grounded, and then connect the other charger wire to that wire or terminal.
- If the battery was not removed from the vehicle, connect the other charger lead to any thick metal part of the engine block or frame.
Step 9. Plug the charger into a power outlet
The charger should be equipped with a plug that fits into a grounded outlet. Leave the battery connected to the charger until it is fully charged; to understand this you will have to inquire about the time it takes to fully recharge your battery, or check the charger indicator which indicates that it is fully charged.
Use an extension cord only if absolutely necessary. If you really need an extension, it must also be equipped with grounding and must not require the use of a reduction to connect the charger, as well as being equipped with a cable with a sufficiently large diameter to withstand the amperage requested by
charger.
Part 3 of 3: Unplug the Charger
Step 1. Remove the plug from the socket
Step 2. Disconnect the clamps from the battery
Start by disconnecting the clamp connected to the grounded battery terminal, then proceed with the other.
Step 3. Put the battery back in place if you removed it from the vehicle
Step 4. Reconnect the vehicle cables to the battery
Start with the ungrounded terminal, then proceed with the other.
Some loaders have the characteristic of being able to start the engine of a vehicle. If your charger is of this type, you can leave it connected to the vehicle battery when you start the engine; if not, you will need to unplug it before starting the engine. Either way, avoid getting close to moving engine parts if you are working with the hood up or the engine cover removed
Advice
- Charging times for car batteries are based on their capacity, while charging times for motorcycle, garden tractor, and deep cycle batteries are based on the amp-hours they can deliver.
- When you connect the charger clamps to the battery, move them several times in different directions to make sure they are well connected.
- Even if you are wearing safety glasses, move away from the battery when connecting the charger.
- If the battery has non-removable caps, it may have an indicator that shows the condition of the battery. If it indicates that the water level is low, replace the battery.
Warnings
- Remove any rings, bracelets, wristwatches, or any other metal accessories before working with the battery and charger. Any of these could cause a short, melt, and severely burn you.
- Although higher current values will charge the battery more quickly, too high a current value could end up overheating the battery, damaging it. Never exceed the recommended current value for charging, and if the battery gets hot to the touch, stop charging and let it cool before resuming charging.
- Never allow a metal tool to touch both battery terminals at the same time.
- Keep soap and water on hand so you can wash away any leaking battery acid. Wash off the acid immediately if it comes in contact with your skin or clothing. If acid gets into your eyes, rinse them for at least 15 minutes with cold running water and seek immediate medical attention.
