Lithium Battery Depth of Discharge, State of Charge & Capacity

Posted October 15, 2019

So what is depth of discharge, or DOD, state of charge, or SOC, and how do both of these affect your deep cycle lithium battery? We'll cover how to calculate DOD, which is important to determine your battery’s optimal number of cycles. We'll also discuss the differences between lithium and lead-acid batteries when it comes to the rate of discharge and capacity.

What Does Depth Of Discharge Mean?

A battery’s depth of discharge indicates the percentage of the battery that has been discharged relative to the overall capacity of the battery.

How To Calculate Depth Of Discharge and State Of Charge

For example, if you have a 100 amp-hour battery and use only 20 amp-hours you have discharged your battery by 20%, which means your depth of discharge is 20%, and your state of charge is 80%. If you took that same 100 amp-hour battery and discharged it 70% your DOD would be 70% and your SOC 30%. It’s important to know DOD calculations because depending on your battery, the number of cycles will vary based on your DOD.

Lithium Battery Cycle Life vs. Depth Of Discharge

Most lead-acid batteries experience significantly reduced cycle life if they are discharged below 50% DOD. LiFePO4 batteries can be continually discharged to 100% DOD and there is no long-term effect. However, we recommend you only discharge down to 80% to maintain battery life.

Lithium Battery Capacity vs. Rate Of Discharge

Another great thing about LiFePO4 batteries is that the rate of discharge has virtually no effect on the delivered capacity. This is also not the case with lead-acid batteries which have significantly reduced capacity of up to 50% as the rate of discharge increases. Lithium batteries provide 100% of their rated capacity, regardless of the rate of discharge, while lead-acid batteries typically provide less usable energy with higher rates of discharge. What does this mean for you? Ultimately you get more hours of power with a lithium battery.

If you have any more questions about your deep-cycle lithium battery, contact our team of lithium battery professionals so we can help get you on the right track.