If you have a presumably dead battery then it is worthwhile to know how to charge a car battery. Keep in mind that a drained battery may not need to be replaced, there are reasons other than a faulty battery as to why it could be fully discharged. If the battery needs to be charged, there are two methods to do so:
| Charging a Car Battery Through Jump Starting
A car can be started using a second vehicle and a set of jumper cables. After starting, the car’s alternator will recharge the battery as the car is driven for at least thirty minutes. Jump starting is common when a car’s battery has been drained through incidental situations such as leaving the lights, air conditioning, heat or some other power draining accessory on for an extended length of time.
To charge a car battery though jump starting follow these instructions:
1 – The cars will need to be parked close enough together so the jump leads will reach from one car battery to the other.
2 – Once the cars are in position and the bonnets are up, attach the red positive clip to the positive terminal on the car with the dead battery.
3 – Place the other end of the red positive lead to the positive terminal on the second car battery.
4 – Place the black negative lead to an unpainted metal surface on the car with the dead battery.
5 – Place the second black negative lead to the negative terminal on the second car.
6 – Start the working car and allow it to run for a few minutes.
7 – Start the vehicle with the dead battery.
| Using a Charger
Car battery chargers are in expensive and easy to use. It is advisable to check the instructions on the one you use, but in principle they are all similar.
1 – Remove the terminal cables from the battery. You will need a spanner to do this. If you have a main electrical point near the car, for example in your garage, then you may be able to keep the battery in the car if the charge cables reach. Otherwise remove the battery from the car.
2 – Connect the red positive charge clip to the positive terminal on the battery.
3 – Connect the black negative clip to the negative terminal.
4 – Chargers may have a single setting or one setting for fast charge and one setting for slow. Slow charging is the preferable method if time allows, this will provide a better charge of the battery.
5 – When the battery is fully charged, remove the cables, replace the battery in the car and reattach the terminals.
6 – Start your car.
It is important to charge a drained car battery as quickly as possible. Extended periods of discharge can lead to sulfation and reduce the life of the battery.
| How Long Does it Take to Charge a Car Battery?
The length of time it takes to charge a car battery is dependent on:
- Depth of discharge, how discharged is the battery
- The amp hour (Ah) rating of the battery
- The amp rating of the charger
If you have a 60Ah battery, that is completely discharged and a 4 amp charger, then it will take 15 hours (60/4) to fully charge the battery.
By doing checking the voltage with a multimeter (see above) you will be able to determine how discharged the car battery is and how long the charging time should be based on the rating of the charger.
Often charging a car battery overnight is the only option to be sure it has a full charge.
| Car Battery Charging Voltage
As your battery goes through a charging cycle the voltage will go through 3 ‘phases’.
- Acceptance (topping)
By knowing what voltage your battery should be at each stage of charging will help you further diagnose battery issues and provide confirmation that the charger is functioning correctly.
Bulk – During the bulk charging phase the voltage will gradually climb to over 14v before it then levels out. For wet cells it will be around 14.8v and for AGM 14.1v.
Acceptance – During the acceptance phase the voltage will remain steady and constant at, or just above, the top of the bulk phase voltage. Once the acceptance phase is complete many charges will turn off as the battery is charged. Others will go to float charge.
Float – In the float phase the voltage will drop down to a level that is safe to sustain over long periods, the voltage will be in the region of 13.5-13.8v.
| Car Battery Not Charging
If your car battery won’t charge then before you replace it make sure that your charger is OK and that you have allowed sufficient time for it to charge. Remember that if you have a 48Ah battery and only a 1amp charger, then you could be waiting for over a day for it to charge the battery.
If you are sure your charger is working OK and you have left it for sufficient time, and it’s just not charging, then it is time to buy a new one!