Buying batteries is quite a mess because there is no proper information about the battery performance, and backup time is not available on the internet. Also, there are lots of options for batteries available on e-commerce sites, which makes buying batteries online much more of a headache.

Even once I talk about a 150Ah Battery with the owner of the battery retailer shop. And whatever he said about the 150Ah battery was almost wrong, it looks like he never went through the manual of the battery.

In this blog, I will briefly introduce the 150Ah battery and backup time for different classes (C10 and C20) and loads.

Before jumping into the details, you need to know about the 150Ah battery. Here is a short note on the 150Ah battery.

A 150Ah (ampere-hour) indicates that the battery can deliver 15 amps for 10 hours (Class C10) or 7.5 amps for 20 hours (Class C20). This rating shows the battery’s capacity under different discharge rates.

The Battery class (C10 or C20) indicates the discharge rate at which the battery’s capacity is evaluated. A Class 10 (C10) rating implies the battery can deliver its full capacity over 10 hours, while a Class 20 (C20) rating implies it can deliver its full capacity over 20 hours.

This is important for understanding how the battery will perform under different usage conditions and helps in selecting the appropriate battery for specific applications.

The calculation for the capacity in this scenario is:

The calculation for the capacity in this scenario is:

150Ah \20 Hours = 7.5 Amp

Generally, there are only two details you will find on the sticker of the battery other than the warranty, that is the battery voltage (‘V’) and battery rating (in ‘Ah’).

Where Ah or Ampere/hour capacity is the current a battery can provide over a specified period to a specific End of discharge Voltage at a specific temperature. Whereas “End of discharge Voltage” is the level to which the cell voltage is allowed to fall before affecting the load.

Also, the battery voltage is the nominal voltage across battery terminals. Generally, the battery voltage for a 150Ah battery is 12V or 24V.

A 12V, 150Ah battery is the most common battery available in the market over the globe and it is made of 6 numbers 2 V cells with End of discharge Voltage per cell is varied from 1.75 V to 1.8 V. Hence the End of discharge voltage for 12V battery varies from 10.5V (1.75V x 6) to 10.8V (1.8V x 6).

If you try to find the details of “End of discharge Voltage” for the battery on its sticker, you won’t find the same. To get the same, you need to ask for the battery specification from the battery retailer, or you can download the same from the manufacturer’s website.

Following is an example of a battery specification I found on the internet. You may find a completely different format of specification because there is no such standard for the same.

As per the above specification of battery, the capacity of the battery is defined as 150Ah at a 10-hour rate to EOD of 1.8V per cell at 25 degrees Celsius. As you can see, the number of cells is also defined in the above specification, which is ‘6’.

This means that this 12V, 150Ah battery is guaranteed to provide a continuous current of 15A over the complete discharge period of 10 hours (that is 15 Ampere x 10 Hour=150 Ah) and the end of discharge voltage of the battery will be 10.8V (6 x 1.8V per cell) at 25°C.

Watt is the unit of power and the amount of power stored in a battery is equal to the multiple of its Voltage and Ampere- hours, hence 12 volts 150Ah battery is equal to 1800 watts (12×150), 24 volts 150 ah battery is equal to 3600 Watt (24 x 150) and a 48 volts 150 Ah battery is equal to 7200 Watt (48 x 150).

Batteries for home inverters and UPS are rated in Ampere Hours, whereas for mobiles, the same is rated in Milliampere Hours. One Ampere hour is equal to 1000 Milliampere hours, hence, 150Ah is equal to 150,000 [150×1000] mAh.

If you search the internet about a 150Ah battery, sometimes you will find that the capacity of the battery is mentioned as 150Ah at a rate of C10. Where ‘C10’ refers to the guaranteed performance of the battery for 10-hour.

Similarly, the ‘C20’ battery, battery is guaranteed to perform for 20 hours.

To find the guaranteed discharge current of C10 batteries, you need to divide the Ampere-Hour of the battery by 10. Similarly, for C20, for the battery, you need to divide the Ampere-hour of the battery by 20.

But the Ampere-hour of the battery will remain the same in both cases; that is, for the 150Ah Class C10 battery, the battery is guaranteed to deliver a continuous current of 15A for 10 hours. Hence, the Ampere-Hour of C10 will be equal to 15A x 10H = 150Ah.

Also, for the 150Ah Class C20 battery, the battery is guaranteed to deliver a continuous current of 7.5A for 20 hours. Hence, the Ampere-Hour of C20 will be equal to 7.5A x 20H = 150Ah.

But if we compare the discharge ampere of C10 150Ah and C20 150Ah battery for a discharge period of 10 Hours, we will find that the 150Ah C10 battery can deliver 15A of continuous current, which is slightly higher than 13.28A of the 150Ah C20.

Also, a 150Ah C10 battery can deliver 8.11A of current over the discharge period of 20 Hours, which is still higher than the 7.46A of a 50Ah C20 battery.

Table-1 shows the difference between the discharge current of 150Ah C10 and 150Ah C20 batteries with identical EODV (End of Discharge Voltage)

This difference in discharge current for the same period impacts the performance of the battery, like backup time, peak current and battery life.

There are two main differences between a 12V 150Ah battery and a 24V 150Ah battery. First is the voltage across their terminal (that is 12V and 24V), and the Second is the power stored in them (that is 1800 watts for 12V 150Ah and 3600 watts for 24V).

In electricity, the formula of power is Power = Voltage x Current

Hence, the amount of power stored in a 24V, 150Ah battery will be 24V x 150Ah = 3600 Watt-hour (3.6 kWh).

And the amount of power stored in a 12V, 150Ah battery will be 12V x 150Ah = 1800Watt-hour (1.8 kWh).

Refer to the table below for a better understanding of the comparison between the power store in 12V 150AH and 24V, 150 Ah batteries.

This means that for a similar load 24V, 150Ah battery will give twice the backup time as compared to 12V, 150Ah. And for similar backup time 24V, 150Ah battery can run twice the load as compared to 12V, 150Ah.

This makes the 24V battery a clear winner, but before jumping to a conclusion that a 24V battery is better than 12V after a comparison of price and power stored in them. You need to understand that to charge as well as for extracting power from a 24V battery you will also need a 24V inverter. And the price of a 24V inverter is higher than that of a 12V.

Also, you cant charge a 24V battery from a 12V inverter, but you can charge two 12V batteries (after connecting them in series) from a 24V inverter.

There are other reasons like availability of 24V battery as well as 24V inverter is very low as compare of 12V battery and inverter for most of the countries. Making going with a 24V battery instead of a 12V battery could be a bad decision.

So, you should check the availability of a 24V inverter before buying the 24V battery.

The backup time of the 150Ah battery depends upon the discharge rate of the battery. This means the faster your discharge battery the less backup time you will get.

Let us compare the backup time of the 150Ah C10 and 150Ah C20 battery

Backup Time for C10 battery:

Refer table below, you can see the discharge rate of 12V, 150Ah at a 10-hour rate to EOD of 1.8V per cell at 25 degrees Celsius

From the above table, you can see that 12V, 150AH C10 (at a 10Hour rate) gives only 97.98Ax1Hour= 97.98Ah (that is, it can withstand 1139.16 Watt of Power for a continuously one Hour) if you completely discharge it within 1-hours.

But if you completely discharge it in 20 Hours C10, 150Ah battery will give 8.11Ax20Hours = 162.2Ah (that is, it can withstand 97.8 Watt of Power continuously for 20 Hours)

Due to the efficiency of the inverter (which is 90% to 95% for a high-end sine wave inverter) the AC output power will be 5% to 10% lesser than the battery output.

Also discharging the battery below 50% again and again will damage the battery life. That’s why to get the high life of battery 150Ah, C10. It should not be loaded more than 622.4Watt for more than 1 Hour.

Backup Time for C20 battery:

Refer below table you can see the discharge rate of 12V, 150Ah at a 20-hour rate to EOD of 1.8V per cell at 25 Degree Celsius

From the above table, you can see that 12, 150AH C20 (at a 10 Hour rate) gives 89.29Ax1Hour = 89.29Ah (that is, it can withstand 1024 Watt of Power continuously for 1 Hour) if you completely discharge it within 1-hours.

But if you completely discharge it in 20 Hours battery will give 7.46Ax20Hours = 149.2Ah (that is, it can withstand 90 Watt of Power continuously for 20 Hours)

Also, discharging the battery below 50% again and again will damage the battery life. That’s why to get the high life of battery 150Ah, C20. It should not be loaded more than 559.4 Watt for more than 1 Hour.

Refer to the below table, which shows the comparison between backup time for C10 and C20 batteries of the same Ampere hour (150Ah), End of Discharge Voltage (1.8V) and terminal voltage (12V).

From the above table, it is clear that C10 batteries provide much more backup time than C20 batteries. And that’s the reason why C10 batteries are preferable to C20 batteries, especially for off-grid solar power plants.

In off-grid solar power plants, you have only 5 to 7 hours of sunshine to charge your batteries and the remaining 17 to 19 hours of power will be provided by batteries.