How Long Does It Take to Charge a Car Battery? Times and How to Do It

Updated Oct 23, 2026 · First published Oct 23, 2026 · 7 min read · By Hassan, Owner of Roadmate Services

The jump worked and the engine is running. Now the battery needs filling back up. How long does it take to charge a car battery? On a charger, a flat battery takes hours: about 5 hours at 10 A to about a day at 2 A for a typical battery, according to charger makers. A drive after a jump only part-charges it, and idling barely helps. The step-by-step for charging it yourself is further down.

Quick answer: how long to charge a car battery

Published market figures from charger makers and a parts store, not Roadmate figures.

Sources: CTEK, Battery Tender, AutoZone. Checked October 2026.

How long to charge a car battery with a charger: 2.5 to 48 hours

CTEK’s rule of thumb is battery capacity divided by charger current. A fully flat 50Ah battery takes about 25 hours at 2 A, 5 hours at 10 A and 2.5 hours at 20 A. Battery Tender gives 24 to 48 hours on a 2 A charger and about 3 to 8 hours at 10 A.

What stretches the time:

• How flat it is. Half flat needs about half the time.
• Battery size. Trucks and big SUVs carry larger batteries.
• Type. AGM batteries need a charger with an AGM setting (see AGM vs flooded batteries).
• Cold. Battery Tender notes that a cold battery charges more slowly.

A 2 A charger is the slow cooker of battery charging: set it up in the evening and check on it tomorrow.

How to charge a car battery with a charger

Charging a car battery at home takes a 12 V charger, an outlet and about ten minutes of setup. Safety comes first: a lead-acid battery gives off flammable hydrogen gas while it charges, so air and no sparks matter more than speed (ODOT battery charging safety). Your charger’s manual comes first if it says something different.

1. Pick a spot with air. Outside, or in a garage with the door open. No smoking, no flames and no grinding nearby.
2. Check the battery. Wear eye protection. If the case is cracked, swollen, leaking or frozen, do not charge it. Heavy white crust on the terminals? Clean it first (how to clean battery corrosion).
3. Switch everything off. Ignition, lights and accessories off. Keep the charger off and unplugged while you connect it.
4. Red clamp first. Connect it to the positive (+) terminal.
5. Black clamp second, away from the battery. Clamp it to bare, unpainted metal on the engine block or frame. Any spark then happens away from the battery gas.
6. Set the charger. Choose 12 V and the battery type: standard (flooded) or AGM. An AGM battery needs the AGM mode. For a full charge use a low-amp setting, not the “engine start” or boost mode, which is only for a quick start. Then plug in and switch on.
7. Know when to stop. A smart charger shows full or drops into maintain mode by itself. A basic charger does not, so use the times above and do not leave it on for days. If the battery gets hot, hisses or smells like rotten eggs, switch off and unplug.
8. Disconnect in reverse. Charger off and unplugged, black clamp off, then red.

If the battery is out of the car, both clamps go on its terminals, still red first. Taking it out? See how to disconnect a car battery for the safe order. No charger at all? To recharge a car battery without one, a jump and a long drive is the other route, covered next.

The charger manual is the rare manual worth reading. It is shorter than the terms and conditions on your phone, and far more useful.

How long to recharge a car battery by driving

AutoZone puts it at 30 to 60 minutes of highway driving for a slightly drained battery, and several hours for a seriously flat one. Steady highway speed beats stop-and-go, because the alternator puts out more at higher engine speeds.

So a loop of I-270 does more for the battery than a crawl down High Street at rush hour. Your playlist may disagree.

Will idling charge a car battery?

Slowly, if at all. At idle the alternator makes less power, and the heater, lights and defroster use much of it. AutoZone says idling charges the battery, just not very efficiently.

If you must idle, switch off everything you do not need. Idling in the driveway charges a battery about as well as staring at your phone charges your phone.

Does the alternator charge the battery?

Yes, whenever the engine runs. It runs the car and tops the battery back up after each start. It is not built to rebuild a fully flat battery.

A battery that keeps going flat can also mean a charging problem, which a jump alone will not show. Our guides to signs of a bad alternator and why a car battery keeps dying go deeper. The alternator is the quiet coworker who only gets noticed when it stops showing up.

Can a completely dead battery be recharged?

Often, if it is not old or damaged. One that is swollen, leaking or dies again within days probably will not hold a charge. AAA puts typical battery life at 3 to 5 years; see AAA’s battery life guide. If yours is that old, our guide to what to do when your car battery dies covers the next steps.

This is where we will be honest: a jump and a short drive is not a full charge, and a battery that will not hold one needs replacing, not another jump. Charging a tired battery overnight is easy. Remembering to unplug it before work is the hard part.

Rather not wait hours? Help in Columbus

If the car will not start, we come to you with a booster pack, no second car needed. A jump start in Columbus is $75 to $150 (estimated range).

After every jump we test the battery, the alternator and the charging system, so you know whether a drive will do or the battery is done. If it is, we offer a battery replacement on site, quoted by phone. Average arrival is about 32 minutes, depending on traffic, weather and location, 6 AM to 8 PM daily. We do not charge electric vehicles on the road: an EV with an empty main battery gets a flatbed tow to a charger or home.

Doing it yourself? See how to jump a car safely or, if the car only clicks, what the clicking means.

Frequently asked questions

The bottom line

A flat car battery takes hours to charge: roughly 5 hours on a 10 A charger and a day or more on a 2 A trickle charger. Charge it with the red clamp on first, the black on bare metal and the charger set for your battery type. A drive after a jump only gets it partway, and idling barely moves the needle. If it keeps going flat, get it tested before you buy anything.

Here is to a battery that fills up faster than your coffee cup empties.