How to Recharge a Car Battery

To recharge a car battery it must be done on the same as it was discharged. Before attempting to recharge the car battery always make sure that the battery is at room temperature (60 °F to 80°F). Also, when it is extremely cold remove the battery from the car and bring it indoors to allow the battery to become warm before begin the charging.

How to recharge a car battery by slow charging

Slow charging is done if the battery was discharged slowly over a long period of time such as standing loss while in storage, lights of the car were left on, the voltage regulator setting was too low, and small short slowly draining the battery. In this case, recharge the battery slowly at 6 to 10 amps for up to 8 to 10 hours.

A good rule of the thumb slow charging rate – charge at a rate equal to one-half the number of plates per each cell.

Example:
A 13 plate cell should charge at 7 amps.
A 7 plate cell should charge at 4 amps.

How to recharge a car battery by fast Charging

Fast charging is done on the battery if it was discharging rapidly such as during a starting failure you cranked the engine until the battery went dead. In this case, the battery must be charged using a fast charger at a rate of up to 40 amps for a 12-volt battery or 70 amps for a six-volt battery for a maximum of 1 to 2 hours.

Safety Precautions When Doing a Fast Charging

Keep a careful watch on the battery that is being fast-charged. When the battery temperature reaches 125 °F or when the gasses are seen coming out of the battery then reduce the rate of charge to a slow charge rate.

Battery Damage That can Result from Fast Charging

Warp and buckle plates can cause by overheating, this could damage the separator and could cause a short circuit within the cell. Reduce battery capacity caused by violent bubbling and gassing action of the electrolyte, this could wash the active material from the plates and could cause an internal short.

How to Test an Alternator
An automobile has many electrical devices, such as the starting system, lights, radio, etc. These devices are operated by the electric current supplied from the battery and alternator. The amount of power generated depends on the alternator specification and engine speed
Learn more: How to Test an Alternator

Exploding Batteries

Batteries can and will also explode, and sometimes with considerable force. A few simple precautions will prevent battery explosions.

A battery by itself will not explode unless a spark or flames has ignited the hydrogen and oxygen gas.

Keep sparks, flames away from batteries while charging.
Keep your charging area well ventilated. Turn off the battery charger before disconnecting charger clamps.
Keep electrolytes up to the proper level. This means a less volume of gas can collect in a full cell.

Batteries generate gas in in-vehicle as well, since the alternator has been recharging the battery. Again, keep sparks, flames, and cigarettes away when working on a battery in a customer automobile.

How to disconnect a car battery to avoid sparks depends on what to disconnect first. Before you start disconnecting the battery cable turn off all lights and accessories then disconnect the ground cable first.