 # How to calculate the capacity of the batteries?

How much power do batteries need? Here we explain how to calculate the capacity of a battery so that it is suitable for your installation. Normally, in the technical data sheets of the batteries you will be able to see the capacity, but we will explain it to you in more detail.

In the battery, its capacity is indicated, expressed by the code ‘CX Y Ah’ , where CX is the discharge time and Ah (Amps Hour) is the discharge current, always for a fixed voltage. For example, if we have a C10 50Ah battery, it means that the 50Ah battery can be discharged for 10 hours .

This code is usually expressed in batteries for times of 10, 20 and 100 hours, that is, C10, C20 and C100 with their respective currents.

How do you calculate the amps we need to provide power to a device?

1st step. Calculate the capacity in amp-hours according to the formula:

C = X T

Where X are the amps that the application needs and T is the time in hours that we want it to work. For example, if we want to power a pump that consumes 140mA for 24 hours, we will perform the following calculation:

C = 0.14 amps • 24 hours = 3.36 Ah

2nd step . Calculate the capacity that we will need from the battery, without completely discharging it . Full downloads, down to zero, are not recommended. For example, if a lead acid battery is going to be used in many cycles , it is not recommended that it extract more than 50% of its charge , that is, that there always be 50% of the charge in the battery. In this way the battery degrades less and its useful life is extended. The following calculation is made, where C is the capacity, taking these considerations about the battery:

C* = C/0.5 ; C* = 3.36/0.5 = 6.7Ah

So we will need a battery that provides us with a capacity of 7Ah.