Jumping in your car, turning the ignition key and nothing happening is one of the worst things possible. It usually happens when you’re in a rush, of course!
You need to get your car started and get going. But how long should you drive after jump-starting your vehicle? Well, definitely at least a few miles, so that your battery has enough charge to start the car again. But how long does it take to charge your battery fully after it has gone flat?
We’ll try to answer these and other questions in the following brief article.
Recharging Your Car Battery After a Jump Start
Using the Car’s Alternator
Recharging your car battery using the alternator might seem like the ideal solution, but it’s far from it. The alternator is only designed to supply enough power to maintain your battery at full charge and power your car’s accessories. This is a very different proposition to recharging a dead battery, which can draw a very high current.
Even if you go for a very long drive of several hours, the alternator can never fully charge your battery.
The other problem is that trying to charge a flat battery puts a heavy strain on your alternator. It wasn’t designed to supply such a large current. Doing this once in a while, in an emergency, won’t be an enormous problem. If your battery is weak, and you keep jump-starting your car, it could affect your alternator working life.
A weak battery will also strain your starter motor. As the voltage supplied from a soft battery drops, it requires a higher current to compensate. The starter motor wasn’t designed for the higher current, and you can easily damage it.
It’s an excellent idea to test your battery and replace it if it’s terrible. You can test a battery with a load tester. If you don’t have one, take it to a workshop or parts store.
If your battery is okay but has just run flat, it’s best to charge it with a battery charger.
Charge with a Battery Charger
Recharging your battery with a modern smart battery charger is the recommended action after a jump start. Older trickle chargers are not designed to switch off automatically at full charge. Trying to charge a battery that is already fully charged will quickly damage it.
Smart chargers can include a range of useful features:
- Overcharge protection to prevent damaging your car battery.
- Maintenance mode, to keep your battery fully charged automatically.
- Deep cycle modes that can help to revive a completely dead battery.
Charging time for your battery will vary. This depends on the size of the battery in amp-hours and the power your charger can deliver.
An average car battery is around 50 amp-hours. At a rate of 5 amps per hour, it will take 10 hours to charge your battery fully. You can charge modern AGM batteries at a higher rate than traditional wet filled batteries. They will often accept 10 amps or more.
- Charging time for a 50 amp AGM battery at 10 amps is 5 hours.
- Charging time for a 50 amp wet battery at 5 amps is 10 hours.
Using a modern automatic charger is recommended. It takes the guesswork out and prevents overcharging of your battery.
Should I Replace My Car Battery After a Jump Start?
Not necessarily. Before you rush to replace your battery, you first need to work out why it went flat in the first place. If you don’t, you might have the same problem in two days.
There are many reasons why your battery lost its charge:
- Electrical item, such as an interior light left on overnight in your car
- A faulty alternator.
- A poor connection between the alternator and your battery.
Batteries can be expensive to replace, so it’s worth making sure that it is the fault. The following should help:
- If the battery is over 5 years old, it is definitely worth changing.
- Have the battery load tested to make sure it holds a charge? This is a good indication of whether it’s healthy or not.
- Measure the voltage at the battery with your engine running. It should show about 14 volts. This indicates that the alternator is supplying enough power to recharge your battery.
Tips and Warnings
Your battery has a finite life, and you can usually expect it to last between three to five years. After this point, you are living on borrowed time.
A few simple tips can help give your battery the longest possible life:
- To give the alternator the best chance of charging your battery after jump starting, turn off all unnecessary electrical items. This includes things such as air conditioning, radio, interior lights, etc.
- Check the alternator belt regularly. If you don’t know how to do it, ask a friend or a car mechanic.
- Check and clean the battery terminals. Corrosion on the battery terminals or cables will prevent the battery from charging correctly. It can also cause starting issues.
- If you don’t drive the car regularly, disconnect the battery. Even with everything switched off, there is a constant drain on the battery, which will flatten it over time.
- Invest in a modern smart charger. These will keep your battery at the optimum level of charge and switch off automatically. They can also revive batteries that have run completely flat.
A flat battery on your car is a pain, and there’s no question of that. But lookout for telltale signs, such as poor starting, dimming headlights, or anything out of the ordinary.
At the first signs of trouble, get the battery checked. Leaving it will only cause more pain in the future!