How Long Does It Take to Charge a Car Battery at 6 Amps?

Cars' batteries are charged via onboard alternators combined with the control electronics and generally, they are not charged outside the vehicle.

However, from time to time, one has to remove them from the vehicle and charge them using a battery charger. Thus, many people ask how long does it take to charge the car battery at, let's say, 6 Amps?

Published: January 11, 2021.

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Little Bit About Car Batteries

Despite lithium batteries becoming more and more popular, car batteries are still mostly lead-acid batteries, commonly wet/flooded, enhanced wet/flooded, Absorbent Glass Mat (AGM), or Gel-Cell batteries.

Also, most car batteries are optimized for starting/cranking applications with only a few trucks/SUVs featuring dual-purpose batteries.

The most common car battery is a 12V (volts) lead-acid battery, featuring a nominal capacity of 40-70 Ah (Amp-hours).

Wet/flooded lead-acid batteries are/were the most common ones, with Enhanced Wet/Flooded and AGM batteries becoming more and more popular. Gel-Cell batteries are not commonly designed as starting batteries, but since most AGM and Gel-Cell batteries are of the spill-proof design, they are gaining in popularity, especially in dual-battery electric systems.

Car Battery Chargers

If the car battery must be recharged using a battery charger, it is highly recommended to recharge the battery using a smart/intelligent battery charger that is programmed to analyze the battery first and only then to start the charging process - this is very important in situations where starting batteries must be recovered from deep discharge conditions.

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Smart battery chargers feature different charging modes and may and should be set according to the battery being charged: wet/flooded, AGM, or Gel-Cell.

All three battery types feature similar, but not exactly the same charging voltages and temperature charging coefficients - hence it is very important that the battery charger is set properly and that it features a temperature sensor.

When the battery charging process starts, the battery charger analyzes the battery first and adjust be battery charging process, including the desulfation phase (if required), warming up, bulk phase, absorption phase, float phase, equalization phase (if required), and maintenance phase/mode.

Note: not all smart battery chargers feature all these charging phases/stages.

Battery Charging Time

When the battery is being charged using, for example, a 6 Amps battery charger, actual charging time depends on the battery capacity, Depth of Discharge (DoD%), battery condition, etc.

On average, approximate charging time may be calculated using a formula:

T(h) = Battery Capacity (Ah) * DoD / Battery Charger Current (Amps)

However, since smart battery chargers don't start the charging process right away and don't charge the battery all the time with maximum current, charging time is a little bit longer - and this 'little bit longer' depends on the individual charger, but generally it is rather short, compared with the approximate charging time.

For example, the following chart lists average battery charging times - batteries are discharged down to 50% DoD and are being charged using smart lead-acid battery chargers:

Capacity 40Ah 50Ah 60Ah 70Ah
Charging Time ~3.5h ~4.5h ~5.5h ~6-6.5h

Again, smart battery chargers don't charge the battery all the time with their maximum current, hence the charging time is a little bit longer than simple calculation using required charge (Ah) and maximum charging current (A).

6 Amps smart battery chargers may also be used for charging of larger batteries, but the charging process may last too long - if You have larger batteries, for example, 100Ah, then larger battery chargers are recommended (10-15 Amps, for example).