Life Cycles, Depth of Discharge and Ideal State of Charge on LifePo4 Batteries

Jun 07, 2023 by SANFOU

DOD: 

Depth of discharge means the degree of battery discharge, usually expressed as the percent rate. This rate indicates how much the maximum capacity value of battery can completely be consume. The real DOD of LifePo4 batteries is 100% also expressed as 1C, the capacity can be fully discharged within 1hour. But lead-acid battery is only 0.1C, which need 10 hours to be completely consumed. 0.2C means the discharge capacity drain to 100% can be achieved only within 5 hours. Please notice that LifePO4 batteries can continue to discharge to 100% DOD, but we suggest you to discharge to 80%(better not pass 80%), to better maintain the battery service life.

SOC:

The minimum stage of charge of the battery, the ideal charge rate always below the DOD, Take the case that if you have the 70% batteries depth of discharge, that mean the batteries capacity can only be consumed 70% .The SOC of the batteries will be 30%, and if you charge over 30%, it may cause the issue of short circuit.

(Calculate: DOD=1-SOC)

Life cycles:

In fact, life cycles can not just based on the charge and discharge rate, there will be other factors like, temperature, bump or shock or other external conditions, so it is unrealistic to calculate the precise data of life cycles. There will be a regular rule that the life cycles and the times of charge and discharge cycles of the LifePo4 batteries depends on how much capacity you generally use. If you use the low battery discharge percent rate, the times of charge and discharge cycles will be increased simultaneously, you will gain more useful cycles than let the battery capacity drain to DOD 100%. Can easily to  understand that the lower the DOD reach, the more charge and discharge cycles of the battery.

Test Method:

  1. Based on without damaging your battery, let your battery capacity drain to 0%.
  2. Buy a kill-a-watt meter or meter to calculate the DOD and SOC to check the data.
  3. Charge your battery to reach the 100% capacity and let it cool.
  4. Connect which appliance you want to test with battery, to check the discharge capacity change in the different stage.
  5. Don’t forget to make a record by your telephone or camera.

Hope this article is helpful for you!