How Long Does It Take To Charge A Car Battery?
With so many battery sizes, capacities, battery types and even chemistries, many people wonder how long does it take to actually charge a car battery completely.
Car battery charging time depends on many things, with the most important being battery capacity, condition and age, current state of charge, local temperature and similar.
Car Battery Capacity and Type
Depending on the size of the car/truck/SUV and its engine type (gas, diesel) and amount of builtin electronics, car battery capacity generally ranges from 50-60 Ah to 120+ Ah, with rarely few models having batteries out of this range.
Most car batteries are flooded, gel-cell or AGM starting batteries with some car models having dual purpose batteries due to the various electronic and electric systems that has to be powered while the engine is turned off.
Lithium-ion drop-in battery replacements are rarely used, but they should come with Battery Management System (BMS) that support charging via onboard alternator and most common lead-acid battery chargers. However, since features and performances of these batteries heavily depend on BMS, each lithium-ion battery should be treated differently. If you have such battery, check and double check its documentation regarding charging and even reconditioning, provided by battery manufacturer.
Car Battery Charging Current
While the battery is mounted in the car, it is charged with alternator and charging controller that ranges from just few diodes/capacitors (if any) to intelligent, programmable, microprocessor controlled onboard charger that monitors the battery condition and charge it accordingly - or at least, limits the charging current/voltage.
Too strong charging currents may damage the battery, cause gases venting out (which may be of serious issue for AGM/Gel-Cell batteries) and in the end, it may even short-circuit individual cells.
On the other hand, too small charging currents may degrade performances of the deeply discharged battery after certain number of charging/discharging cycles. However, car batteries are used as standby/float batteries and NOT as cycle batteries.
For short, if the car battery is charged by intelligent battery charger, one should go for a current that is able to fully charge the battery in 5-10 hours.
Car Battery Charging Reference Chart
The following chart lists approximate charging times of the car batteries discharged down to 80% by battery chargers featuring different charging currents.
|Battery Capacity||2 Amp||4 Amps||6 Amps||8 Amps||10 Amps||15 Amps||20 Amps||40 Amps|
Again, this is just an approximation - different batteries accept the charge differently, and what is most important, intelligent battery chargers test the battery condition and charge it in several phases, commonly including Analysis, Desulfation, Soft Start, Bulk Charge, Absorption, Battery Test, Conditioning and Maintenance phase.
Rapid battery charging can save a lot of time, but also, it can damage the battery in the long run. If possible, avoid charging the battery in less than 4-5 hours, although there are battery models that support full charging in 3 hours.
Also, charging the battery longer than 12-15 hours takes plenty of time and can cause unwanted changes of battery plates surfaces, at least for starting batteries - most solar batteries are design to accept charge slowly, or at least over MPPE charge controllers.
So, if you are looking for a good car battery charger, go for the model with output current in the 6-10 Amps range - even better if the output current may be adjusted.
How Long to Charge a Car Battery at 6 Amps
5 or 6 Amps are typical charging current of smaller battery chargers and depending on the battery condition, capacity, type, age, etc., a good 6 Amps battery charger may charge car battery discharged down to 80% DoD (or 20% SoC):
- 40 Ah car battery: ~7 hours,
- 50 Ah car battery: ~9 hours,
- 60 Ah car battery: ~10 hours,
- 70 Ah car battery: ~12 hours,
- 80 Ah car battery: ~14 hours,
- 90 Ah car battery: ~15 hours,
- 100 Ah car battery: ~17 hours,
- 110 Ah car battery: ~19 hours,
- 120 Ah car battery: ~24 hours.
Personally, I would never charge modern car battery with the battery charger that requires more than 10-12 hours to charge the battery completely. Call me lazy, narrow-minded, etc, but ...
For short, 6 Amps battery charger should be used for car batteries up to 80-90 Ah.
How Long to Charge a Car Battery at 10 Amps
10 Amps battery chargers are intended for medium sized car batteries, although they can be used for both smaller and larger batteries.
Required time, on average, for 10 Amps battery chargers to charge car battery discharged down to 80% DoD (Depth of Discharge, or 20% of SoC - State of Charge) in hours is battery capacity divided by 10. For example:
- 40 Ah car battery: ~4 hours,
- 50 Ah car battery: ~5 hours,
- 60 Ah car battery: ~6 hours,
- 70 Ah car battery: ~7 hours,
- 80 Ah car battery: ~8 hours,
- 90 Ah car battery: ~9 hours,
- 100 Ah car battery: ~10 hours,
- 110 Ah car battery: ~11 hours,
- 120 Ah car battery: ~12 hours.
Again, these are just approximate charging times, because battery condition and battery charger model, dictate how long will individual charging phases last, especially charging phases prior Bulk Charge phase.
Personally, if you need a good car battery charger, go for the models in 8 to 10 Amps range.
How Long to Charge a Car Battery at 40 Amps
Charging car batteries with strong currents, for example 40 Amps, can significantly shorten the charging time, but it may also shorten the battery operating life, especially the operating life of smaller and medium batteries.
However, some 'Stop&Go' (or 'Stop&Start) lead acid batteries are designed to both provide and to accept large currents required for frequent starting/cranking of the car engine and for fast charging while the engine is turned on.
Additional strain of these batteries are all onboard electric and electronic systems that are turned ON, while the engine is OFF - lights, radio, fans etc.
'Stop&Go' batteries may be wet (Advanced Flooded Battery (AFB) or Enhanced Flooded Battery (EFB)) or AGM (Absorbent Mat Glass), but they all feature high charging currents as well - and this must be explicitly stated by their manufacturer.
If the manufacturer states that their battery or batteries may be charged by 40 Amps charger, go for it. If not, 40 Amps chargers should be used only for 120 Ah, preferable for 150+ Ah batteries (Group 4D, Group 8D and similar large batteries).
How Long to Charge a Dead Car Battery
If the battery is dead and the battery charger doesn't 'want' to charge it, then the battery is dead, right?
Well, yes and no. Problem with common battery chargers, even with some 'smart' ones is that they can't detect 'too low battery voltage' during Analysis charging phase.
A good battery charger is able to detect such battery condition and will try to bring the battery to life during Desulfation charging phase by using short current pulses and once the battery is brought back to life, the battery charger will move automatically to the next charging phase which is usually Soft Start of Bulk Charge.
So, if your car battery appear dead, with voltage as low (or lower) as 7-8 volts for example, connect it to the smart charger and let it do its job - if the cells didn't short-circuit, there is a great chance that the charger will recharge even such battery.
Note: regardless how good the charger is, such deep discharge event may cause irreversible damage to the battery in the form of decreased capacity and/or lower cranking/starting Amps.
Depending on the battery condition, capacity and nominal charging current of the battery charger, charging of the dead car battery should last slightly longer than regular charging - just let the charger enter the maintenance mode (Trickle Charging), after which it may be disconnected from the battery.
Car Battery Charger End Voltage
Generally, lead acid batteries end charging voltage depends on the battery use and type (wet cells, AGM, gel-cells, at 77°F, 25°C):
- float use: end voltage should be in the 13.5-13.8 volts range,
- cyclic use: end voltage should be in the 14.4-14.8 volts range.
Regardless of the use and type, charging voltage of lead-acid batteries should NOT be above 15 volts.
Since car batteries are used as starting/cranking batteries, their end voltage should be set as for 'float use'.
Note: intelligent battery chargers also include temperature compensation, usually in the -20mV/°C to -30mV/°C range, depending on the battery use/charging.
Long Story Short: Car batteries are vital part of every car with the internal combustion engine and having a battery in good condition is of upmost importance.
But, even new batteries may fail for countless reasons and recharging them using battery chargers is a quick and efficient way of returning them into operation.
Most car batteries may be charged using 8-10 Amps battery chargers and if you are looking for one, go for the smart battery charger model with the charging current in this range.