Calculation of How Long Will a 200Ah Battery Last

what is ah in a battery

When planning for backup power or off-grid energy solutions, knowing how long a battery will last is crucial. A 200Ah (amp-hour) battery is a common choice for many applications, including solar power systems, RVs, and backup power for homes. To accurately determine how long a 200Ah battery will last, several factors must be considered.

This article uses a 200Ah battery as an example to explore the factors affecting battery runtime and provides a detailed method for calculating it. We will explain the relationship between battery capacity and the number of hours household appliances can run, as well as how to predict battery backup time based on energy demand.



Five factors for calculating battery run time

Before the explanation on how long will a 200Ah battery run, it’s necessary to clear one thing up: There is no way to calculate the running time of battery precisely, because it is influenced by many factors.

However, we can consider 5 key factors to estimate the running time as accurately as possible for optimal battery use.


Battery voltage

The voltage in a battery refers to the potential difference between the positive and negative terminals of the battery. But the battery voltage will gradually decrease as the power passes, so we just can use the nominal voltage of the battery(12v, 24v, 36v,48v) to estimate the battery run time.


Battery capacity

Battery capacity, measured in amp-hours (Ah), is obvious from the name, it is Current x Time. According to Charge Conservation, Ah can be interpreted as the amount of charge for charging and discharging in a lithium battery during a certain period of time. A 200Ah battery, theoretically, can deliver 200amps of current for one hour or 20 amps for 10 hours.

Usually, the voltage and ampere-hours together indicate the capacity of the battery, such as 12V 200AH, 12V 100AH. The same voltage of the battery, the higher the ampere-hour, the larger the capacity.

For a more direct understanding, it's practical to convert ah to kwh, because it's a standardized way to measure and compare energy capacities and consumption. This is especially useful when comparing different energy sources or storage systems.


Depth of discharge

Depth of discharge(DoD) is the ratio of the power released from the battery to the rated capacity of the battery.

For example, the rated capacity of the battery is 200Ah, the capacity remaining after discharge is 100Ah, the actual discharge capacity is 100Ah, then the depth of discharge of the battery is 50%.

Usually, the battery with the depth of discharge from 10% to 80% is called shallow cycle discharge battery, and another with the 80% depth of discharge is deep cycle battery.

The two main types of solar batteries in this size range are lead acid battery and lithium phosphate battery. Each has its own pros and cons. Lithium phosphate batteries are more expensive but offer significant benefits, the most notable being their intrinsic deep-cycle capability.


Energy consumption

Energy consumption is the amount of power that your devices use, typically measured in watts (W). To calculate battery runtime, you need to know the total energy consumption of all devices that will be powered by the battery. This includes everything from lights and appliances to electronic devices. Knowing the total wattage of the devices will run is necessary for an accurate calculation.


Efficiency of the inverter

The efficiency of the inverter, expressed as a percentage, indicates how much energy it converts from the battery's DC power into the AC power needed by most appliances. No inverter is 100% efficient; some energy is always lost in the conversion process. Higher efficiency means less energy is wasted, resulting in longer battery runtime.


How to calculate how long will a 200Ah battery last

To calculate how long a 200Ah battery will last, you can use the following formula:

Battery Run Time = (Battery Capacity x Battery Voltage x Depth of Discharge x Efficiency of Inverter) / Energy Consumption


We can estimate the runtime of a battery by either assuming the inverter operates at full rated power or by summing the power of all connected devices. Below, we will demonstrate these two methods to determine how long a 200Ah battery will last.


How long will a 48v 200Ah battery last

Let's calculate the backup time of a 48V 200Ah battery, using the PowMr 48V 200Ah battery (80% Depth of Discharge) paired with a 3000W inverter boasting 95% efficiency.

200Ah deep cycle battery 200ah

Rated at 48v, a 200Ah battery connected to a 3000W inverter(95% efficiency) working at full rated, it will last for 2.432 hours.

200Ah battery run time = (200Ah x 48v x 0.8 x 0.95) / 3000W = 2.432 Hours

Moreover, if solely powering a 400W fridge with this 200Ah battery, it could run for approximately 18.24 hours.

200Ah battery run time = (200Ah x 48v x 0.8 x 0.95) / 400W = 18.24 Hours


How long will a 12v 200Ah battery last

Given that two parallel-connected 100Ah batteries (DoD 100%) form a 12V 200Ah battery system, and are connected to a 2000W inverter for 12v battery (operating at full rated capacity with 92% efficiency), it will last approximately 1.104 hours.

200Ah battery run time = (200Ah x 12v x 0.92) / 2000W = 1.104 Hours

Moreover, if you are using a 12V 200Ah battery solely as a backup to power a small 400W fridge in your RV, it could run for approximately 5.52 hours.

200Ah battery run time = (200Ah x 12v x 0.92) / 400W = 5.52 Hours


How long will a 24v 200Ah battery last

Assume a 24V, 200Ah battery system composed of four 12V, 100Ah batteries (DoD 100%), configured with two batteries in parallel (200Ah) and then connected in series to achieve 24V. This setup powers a 2000W inverter with 92% efficiency.

When the 2000W inverter is operating at full capacity, the 24V, 200Ah battery system will last for approximately 2.208 hours.

200Ah battery run time = (200Ah x 24v x 0.92) / 2000W = 2.208 Hours

If the energy from the battery is used to power a 400W appliance, the 200Ah battery can run for approximately 11.04 hours.

200Ah battery run time = (200Ah x 24v x 0.92) / 400W = 11.04 Hours

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