When the topic of batteries used for renewable energy systems comes up, deep cycle batteries are typically the ones most people have in mind. Deep cycle batteries are basically energy storage units, where voltage is developed through chemical reaction, thus resulting in electricity. These batteries can be discharged and recharged numerous times, while keeping their charge capacity and release capacity practically the same.
There are various different types of deep cycle batteries solar panels use nowadays: flooded batteries, AGM batteries, gel batteries and the most recent ones – lithium-ion batteries. The most common type of deep cycle batteries solar panels use are the flooded batteries. These work in a similar fashion to standard lead acid batteries that we use in vehicles. Gel batteries feature a gel-like substance, while AGM batteries feature acid which is suspended into a glass mat separator. Gel, flooded and AGM batteries are most frequently used in off-grid systems, while lithium-ion batteries are used in both on and off-grid systems.
Regardless of which type you choose, you should pay attention to the volt and amp ratings. The amp rating indicates how much capacity the battery has in terms of chemical energy that can be converted into electrical energy. In other words, the amp rating refers to the discharge rate of the battery, which measures the amount of time it takes for the battery to be fully discharged before it needs to be recharged again.
However, worth knowing is that the battery’s capacity is reduced if the battery is discharged quicker. The stated ratings refer to the discharge rate per hour. So, if the discharge is quicker, the capacity and the amount of cycles is reduced by about 50%. For most residential applications, the energy capacity of deep cycle batteries is referred to by their kilowatt per hour capacity.
Lastly, you need to pay attention to the discharge cycle of the battery. This alone can make buying a deep cycle battery extremely confusing and intimidating, simply due to the fact that all deep cycle batteries are created differently, even if they’re the same type. Your main goal when buying one should be to get as much longevity as possible, which you can ensure by paying attention to the cycle ratings.
The cycle rating basically indicates how many times you can discharge and recharge a deep cycle battery. There are various different benchmarks to determine, such as the IEC 896-2, which is based on a 100% discharge. However, discharging a battery 100% is not recommended, as this might decrease the battery’s life-span. Regardless, it’s a good baseline indicator for comparing different brands or different models from the same manufacturer.