Depth of discharge, often shortened to DoD, describes how much of a battery’s capacity has been used. If a battery is discharged to 60 per cent DoD, 60 per cent of its rated capacity has been drawn out.
DoD matters because batteries age through charge and discharge cycles. The deeper the regular discharge, the more stress is placed on many battery types.
Lead-acid and AGM batteries are usually kept to shallower discharge if long life is the goal. That means a large part of their labelled capacity is not treated as everyday usable energy.
LiFePO4 batteries tolerate deeper discharge far better, which is one reason they are popular in portable and vehicle power systems. More of the battery’s rated capacity can be used without the same penalty.
When comparing systems, do not just look at total capacity. Look at usable capacity. A smaller lithium system can sometimes deliver more practical usable energy than a larger lead-acid setup.