Battery charge time calculator
A 60Ah car battery at 50 percent takes about 3.6 hours on a 10A charger and about 18 hours on a 2A charger. Charge time is the amp-hours to replace, times about 1.2 for losses and the slow finishing stage, divided by charger amps.
Charge in a ventilated space and never charge a frozen battery.
hours = battery Ah x (1 - state of charge) x 1.2 / charger ampsThe 1.2 factor covers charging losses and the absorption stage, when a smart charger tapers current near full. A sulfated or damaged battery may never reach full; if it will not hold 12.4V a day after charging, have it load tested.
Chargers matched to this battery
Prices from Amazon at the time of writing; they change often.
How long does a car battery take to charge?
Hours for a 60Ah battery from each resting voltage at common charger ratings.
| Resting voltage | 2A | 4A | 6A | 10A | 25A |
|---|---|---|---|---|---|
| 12.4V (75%) | 9.0 h | 4.5 h | 3.0 h | 1.8 h | 0.7 h |
| 12.2V (50%) | 18.0 h | 9.0 h | 6.0 h | 3.6 h | 1.4 h |
| 12.0V (25%) | 27.0 h | 13.5 h | 9.0 h | 5.4 h | 2.2 h |
| 11.8V (5%) | 34.2 h | 17.1 h | 11.4 h | 6.8 h | 2.7 h |
What charger size do I need?
For recovering a flat car battery overnight, 6 to 10 amps is the practical range: a 60Ah battery at 50 percent is full in 4 to 6 hours at 6A. Larger 15 to 25A settings suit truck batteries and shop use. A maintainer of 1 to 2 amps is for keeping a stored vehicle topped up, not for recovering a dead battery quickly.
Match the charger to the battery chemistry. AGM and lithium batteries need a charger with those modes; a charger without them can undercharge an AGM battery or damage a lithium one.
Frequently asked questions
How long does it take to charge a car battery with a 10 amp charger?
A 60Ah battery at half charge takes about 3.6 hours at 10 amps, and a nearly flat one about 6.8 hours. Smart chargers slow down near full to avoid overcharging, which is why the last 10 to 20 percent takes longer than the first.
Can I charge a car battery with a trickle charger?
You can, but slowly. At 1.5 amps a half-charged 60Ah battery needs about 24 hours. Trickle chargers and maintainers are designed to hold a charged battery at full during storage; for a flat battery a 4 to 10 amp charger is far quicker.
How do I know when my car battery is fully charged?
A smart charger switches to maintenance or float mode and says so. With a voltmeter, let the battery rest for a few hours off the charger: 12.6 to 12.7 volts is full for a flooded or AGM battery. If it falls below 12.4 volts within a day, the battery is likely failing.
Is it better to charge a car battery slowly?
A moderate rate, around 10 to 20 percent of capacity per hour, is kind to the battery and quick enough to be useful. Very high rates heat the battery and cause gassing. Modern smart chargers manage the rate automatically, so the main choice is how quickly you need the car back.