When considering solar cell options, you need to compare different lithium batteries based on capacity, depth of discharge (DOD), battery life, and more to find the best battery for your PV system based on your needs.

1. Capacity

Capacity is the total amount of electricity that a solar cell can store. This data is usually measured in watt-hours (Wh) or kilowatt-hours (kWh).

2. Depth of Discharge (DOD)

The depth of discharge (DOD) indicates the battery capacity used. The higher the DOD, the more usage you get from the battery capacity. Most solar batteries come with a recommended DOD to keep the battery healthy. Lithium ion batteries are deepcycle batteries and have up to 100% DOD, meaning you can use more of the energy stored in lithium-ion batteries without recharging as often as you would with other batteries. This also gives them a long service life and capacity is 25-50% higher than similar lead acids.

3. Cycle Life

Cycle life is the number of charge and discharge cycles that a battery can complete before it loses performance. Lithium iron phosphate batteries have more than 2000 cycles, while lead-acid batteries typically only reach between 500 and 1200 cycles. Assuming that one cycle is used each day, then a battery with a cycle life of 2000 retains its performance for five and a half years; a battery that boasts 4000 cycles can be used for more than ten years.

4. Continuous Charging and Discharging Rate

The charge-discharge rate refers to the constant current value output by the battery, when it is charged from an empty state to a fully charged state or discharged from a fully charged state to an empty state, within a specified time. For example, the Renogy 12V 100Ah Smart Lithium Iron Phosphate Battery has a rated capacity of 100Ah and can be discharged for 1 hour at a 100A discharge current, known as 1C discharge. Additionally, the Renogy 12V 100Ah Smart Lithium Iron Phosphate battery with a self-heating function will automatically start running when the battery temperature drops below 41°F (5°C) while charging to ensure excellent battery performance.

5. Battery Life and Warranty

If you’ve owned a laptop or smartphone for a few years, you’ve probably noticed that the battery doesn’t last as long in the years after that as it did when it first started. As each charge and discharge cycle progresses, the battery’s ability to remain charged decreases. Temperature can also affect battery life. High temperatures mean faster reactions, so batteries discharge faster; low temperatures mean batteries have to work harder and charge at higher voltages.

Most batteries come with a warranty that guarantees the battery over a certain number of cycles or for a specified period. Like panels, inverters, or other solar equipment, choosing a well-known manufacturer with a long history is the safest option, as they are more likely to deliver on these promises.