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Writer's pictureYakub Ansari
Aug 19, 20217 min read

What is a 120Ah battery?

Updated: May 23, 2022

Content Table

  1. What is the meaning of a 120Ah battery?

  2. 120ah battery to watts

  3. Backup time of 120Ah battery

  4. Charging of 120Ah battery

  5. Weight of 120Ah battery

  6. 120ah battery life

  7. What size inverter for 120ah battery?

  8. 12V 120Ah Vs 24V 120Ah

  9. 120Ah vs 100Ah

  10. 120Ah vs 120Ah

  11. 120Ah vs 200Ah

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What is the meaning of a 120Ah battery?

The term "120 Ah" means a battery that is guaranteed to produce a constant current of 12A throughout a 10-hour discharge time at a room temperature of 25 degrees celsius (12A x 10h =120 Ah) if the battery is of Class C10.


and for Class C20 battery it will be guaranteed to provide a continuous current of 6A over the discharge period of 20 hours (6A x 20h =120 Ah). Class 10 and Class 20 batteries are also called 10hours and 20 hours batteries respectively.

120Ah battery is available in WET, AGM and GEL construction, Click here to learn more about different construction of batteries.



Above is the specification of a 12V 120Ah, AGM battery. From the above specification, you can see that the nominal capacity of the battery is rated as 120Ah@10hours-rate to 1.8V per cell @25 degrees celsius.



120ah battery to watts

Watt is the unit of power and it represents the amount of power stored in a battery. Theoretically, the amount of power stored in a battery is equal to the multiple of battery Voltage with battery Ampere- hours, hence the amount of power stored in 12 volts 120Ah battery is equal to (12x120=) 1,440 watts, in 24 volts 120 ah battery is equal to (24x120 =) 2,880 Watts and in 48 volts 120 Ah battery is equal to (48x120) 5,760 Watts.


Backup time of 120Ah battery

The backup time of the battery depends upon the discharge rate of the battery. This means the faster your discharge battery the less backup time you will get. In other words higher the connected load lesser will be the backup time.


The backup time of a battery also depends upon the class of battery. Batteries come in different classes of discharge rates. There are two standards of battery discharge rate, that is Class 10 and Class 20.



How long will the 120Ah battery last?

For 1 hour of backup time both class 10 and 20, 120Ah battery can provide backup for an identical load that is 732 Watt to 756 Watt. But for 10 hours of backup time, class 10, 120h battery can provide backup for 140 watts of load. Whereas a class 20, 120Ah battery can provide backup for 100 watts of load.


The following table shows the backup time of a 12V, 120AH battery for Class 10 and Class 20.


Since it is not recommended to discharge a lead-acid battery below 50% again and again, hence the recommended load will be half of what was mentioned above.


Charging of 120Ah battery

The charging time of a battery is directly proportional to the depth of discharge of the battery. The higher the depth of discharge, the longer will be the charging time.


Also, there are limitations on the maximum charging current of the battery. During charging batteries generate lots of heat. Hence battery manufacturers marked the maximum permissible charging current on the battery so that users won’t overheat the battery with a higher charging current.



The maximum permissible charging current of a 12V, 120Ah dry battery is 30A. But the recommended charging current is 10 to 18A.


How long does it to charge a 120Ah battery?

A 100% discharge 120Ah battery can take up to 8 hours to 80% charge at a Charging current of 12 A. Whereas a 50% discharge battery will take up to 4 hours to 80% charge at the same charging current. Charging a 120Ah battery with a lower charging current will increase the charging time of the battery


and charging at a higher temperature will reduce the charging time by eventually increasing the battery temperature.


Refer to the below graph showing the charging time of 120Ah battery with DOD [depth of discharge] of 50% and 100% at changing current of 10A.

Charging of 120Ah battrey

In the above graph charging current of a 12V 120Ah, C10 battery is shown in 0.10 CA and this means 0.10 times of 120AH. Hence the charging current is 12 A (=120x0.10)



How much does a 120Ah battery weight?

The weight of a 120Ah battery depends upon the battery voltage and the technology used to produce the battery. For instance, the weight of a 12V 120Ah dry battery is around 33.5kg, whereas the weight of the 12V 120Ah lithium-ion battery is 10 kg. Whereas the weight of a 24V 120Ah day battery is 103 kg.


Battery life

The life of a battery depends upon two things: the charge cycle concerning the depth of discharge and battery ambient temperature.


Charge cycle concerning the depth of discharge: Deeper the battery is discharged in every charge cycle, the lower will be the battery life. Here, depth of discharge means how deep you discharge the battery.


Battery Ambient Temperature: It is the room temperature at which the battery is stored. Lower the room temperature will increase the battery life. But temperatures lower than 20 degrees celsius also affect the backup time of the battery. The battery gives a high backup time at high room temperature. 25 to 27 degrees celsius is the ideal room temperature to store the battery.


120Ah battery life

With a 100% Depth of discharge, a 120Ah C10 battery can be charged and discharged up to 250-300 times before broken. And with 50% Depth of discharge same battery can sustain up to 450-500 times. However, if you can limit the Depth of discharge below or up to 30% the sustainable cycle of the same battery can be increased up to 1200-1400 cycles.


The life of the battery also depends upon the ambient temperature of the battery surrounding it. At an ambient temperature of 10 degrees Celsius, a 120Ah battery can sustain up to 13 to 16 years at float charging. But at 45 degrees Celsius of temperature, its life will reduce to 3 to 5 years at float charging.



However, the average room temperature of the battery is 30 degrees Celsius and at this temperature, it is given 7 to 10 years of life.


Considering all the points affecting the life of a 120Ah battery, it’s not easy to determine its actual life.


For example, let's say discharge your 120Ah battery 50% for every single day at a room temperature of 30 degrees Celsius, your battery will sustain 450 to 475 days. And if you discharge 50% of your battery for 120 days in a year at room temperature of 30 degrees Celsius. You will get a battery life of 3 to 4 years.


12V 120Ah Vs 24V 120Ah

Theoretically, a 12V 120Ah battery stores 1440 Wh of power, whereas a 24V 120Ah battery stores 2 times more power, that is 2880 Wh. However, a 24V 120Ah battery takes less space as compared to 2 number 12V 120Ah batteries. Also, a 24V 120Ah required a 24V inverter to convert store energy into useful energy, whereas a 120V 120Ah battery required a 12V inverter. A 24V battery is less common as compared to a 12V, also a 24V battery and 24V inverter are relatively expensive.



120Ah vs 100Ah

A 120Ah battery stores 1.2 times more charge than a 100Ah battery of an identical terminal voltage [that is 12V]. Hence a 12V 100Ah battery provides lesser power backup as compared to the 12V,120Ah battery. Also, a 100Ah battery is lighter in weight than a 120Ah battery as well as cheaper too. But a 24V 100Ah battery stores 1.6 times the charge and provides more backup time than a 12V 120Ah battery.


Following are the comparison list between 120Ah and 150Ah battery.

  1. Therocitally a 12V 120Ah battery stores 1440 Wh of power, Whereas a 12V 100Ah battery stores 1200 Wh of power. But a 24V 100 Ah battery stores 2400Wh power.

  2. A 12V 120Ah battery provides more backup time as compared to a 12V 100Ah battery. Refer to the below table showing the comparison between backup time of 120Ah and 100AH battery.

  3. The weight of a 12V 100AH battery is 30.4 kg whereas the weight of a 12V, 120Ah battery is 33.5. Hence there is not much change in weight.

  4. The tentative dimension of a 12 V 120Ah battery is 407mm (L) x 177mm (W) x 225mm (H), whereas the dimension of a 100Ah battery is 330mm (L) x 173mm (W) x 212mm (H).



120Ah vs 150Ah

A 150Ah battery stores 1.25 times more charge than a 120Ah battery of an identical terminal voltage [that is 12V]. Hence a 12V 120Ah battery provides lesser power backup as compared to the 12V,150Ah battery. Also, a 120Ah battery is lighter in weight than a 150Ah battery as well as cheaper too. But a 24V 120Ah battery stores 1.6 times the charge and provides more backup time than a 12V 150Ah battery.


Following are the comparison list between 120Ah and 150Ah battery.

  1. Therocitally a 12V 120Ah battery stores 1440 Wh of power, Whereas a 12V 150Ah battery stores 1800 Wh of power.

  2. A 12V 150Ah battery provides more backup time as compared to a 12V 120Ah battery. Refer to the below table showing the comparison between backup time of 120Ah and 150AH battery.

  3. The weight of a 12V 120AH battery is 33.5 kg, whereas the weight of a 150Ah battery is 50 kg.

  4. The tentative dimension of a 12 V 120Ah battery is 407mm (L) x 177mm (W) x 225mm (H), whereas the dimension of a 150Ah battery is 556mm (L) x 130mm (W) x 296mm (H).




120Ah vs 200Ah

If we compare a 120Ah battery with a 200Ah battery. We will find that a 120Ah battery stores a lesser charge than a 200Ah battery of an identical terminal voltage [that is 12V]. Hence it provides lesser power backup as compared to the 200Ah battery. Also, it is lighter in weight than the 200Ah battery as well as cheaper too. But a 24V 120Ah battery stores more charge and provides more backup time than a 12V 200Ah battery.


Following are the comparison list between 120Ah and 150Ah battery.

  1. Therocitally a 12V 120Ah battery stores 1440 Wh of power, Whereas a 12V 200Ah battery stores 2400 Wh of power.

  2. A 12V 200Ah battery provides more backup time as compared to a 12V 120Ah battery. Refer to the below table showing the comparison between backup time of 120Ah and 200AH battery.

  3. The weight of a 12V 120AH battery is 33.5 kg whereas the weight of a 200Ah battery is 60 kg.

  4. The tentative dimension of a 12 V 120Ah battery is 407mm (L) x 177mm (W) x 225mm (H), whereas the dimension of a 12V 200Ah battery is 522mm (L) x 240mm (W) x 223mm (H).



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