• Capacity in Amps per hour: The Amps per hour of a battery are simply the number of Amps that it supplies times the number of hours that current flows. In a photovoltaic installation, it is used to determine how long can the system work without light radiation to reload the batteries.

This measuring of the autonomy days is one of the most important parts in the design of the installation. Theoretically, for example, a 200 Ah battery may supply 200 A for one hour or 50 A for 4 hours, or 4 A for 50 hours, or 1 A for 200 hours. However, it is not exactly like this, as some batteries, like the automotive ones, are designed to produce quick discharges in short periods of time without being damaged. However, they are not designed for long periods of time of low discharge. This is why automotive batteries are not the best for photovoltaic systems.

• Load and unload Ratios. If the battery is loaded or unloaded at a different pace of the specified one, the capacity available may increase or decrease. Generally, if the battery unloads slower, its capacity increases slightly. If the pace is faster, its capacity will decrease.

• Temperature. Another factor that has an influence on the capacity is the temperature of the battery and its environment. The behaviour of a battery is fixed at a 27 degrees temperature. Lower temperatures reduce their capacity significantly. Higher temperatures produce a slight increase in their capacity, but it may also increase its water loss and decrease the number of cycles in the life of the battery.
  
  
  
• Depth of discharge: The depth of discharge is the percentage of the total capacity of the battery that is used during a load/unload cycle. The "shallow cycle" batteries are designed for discharges of 10 to 25% of their total capacity in each cycle. Most “shallow cycle” batteries made for photovoltaic applications are designed for discharges of up to 80% of their capacity without suffering any damage. Manufacturers of Nickel-Cadmium batteries claim that they can be totally discharged without any type of damage. However, the depth of the discharge affects even deep cycle batteries. The higher is the discharge, the lower is the number of charge cycles that the battery may have.