Depth of Discharge Explained for Home LiFePO4 Packs
Depth of discharge, often shortened to DOD, describes how much of a battery pack's capacity is used before it is recharged. A pack discharged to 70 percent depth of discharge has used 70 percent of its capacity, leaving 30 percent remaining. This article explains depth of discharge in general terms, using the listed cycle conditions on this site as examples. It does not give a depth-of-discharge recommendation for a particular house, because that recommendation needs the load and usage pattern for that house.
What depth of discharge means
Depth of discharge is the complement of state of charge. If a pack is at 100 percent state of charge, its depth of discharge is 0 percent. If it is discharged to 30 percent state of charge, its depth of discharge is 70 percent. Usable energy depends on depth of discharge: a pack with a headline capacity of 10kWh, used to 70 percent depth of discharge, delivers 7kWh of usable energy per cycle under that limit, while the same pack used to 90 percent depth of discharge delivers 9kWh per cycle. That arithmetic is straightforward, but it hides a trade-off between usable energy per cycle and total cycles over the pack's life.
Cycle life is measured under a stated test condition, and the condition matters as much as the headline number. A figure measured at a low discharge rate and a shallow depth of discharge cannot be compared directly with a figure measured at a higher rate and a deeper depth, because the tests differ. A buyer comparing models should therefore read the condition behind each figure, and should ask for any missing detail — rate, depth of discharge, capacity remaining and temperature — before ranking two models against each other.
How DOD affects cycle life
In general, using a smaller depth of discharge leaves more cycles available, while using a larger depth of discharge leaves fewer cycles available. The size of that effect depends on the chemistry, the pack construction and the test condition, so it cannot be reduced to a single rule for every pack. The listed cycle figures on this site illustrate why the condition matters: some models state their cycle figure at a stated depth of discharge, while others state a different condition. Those figures should not be compared without reading the conditions.
Depth of discharge describes how much of a pack's capacity is used before it is recharged. Using a smaller depth of discharge generally leaves more cycles available, while deep discharges use more capacity per cycle. Cycle-life figures therefore only make sense with the test condition attached, such as the discharge rate and the capacity remaining at the end of the test. This site reports cycle life per model with its stated condition, and does not convert one model's figure into a range-wide claim.
DOD in home sizing
When sizing a home pack, the headline stored-energy figure should be converted to usable energy at the intended depth of discharge before it is compared with the household's overnight load. A 12kWh pack used to 70 percent depth of discharge delivers 8.4kWh of usable energy per cycle under that limit, while a 5kWh pack used to the same depth delivers 3.5kWh. Those usable figures, not the headline figures, should be compared with the overnight load. A buyer who compares headline figures alone may choose a pack that looks sufficient on paper but does not cover the night at the intended depth of discharge.
For a business enquiry, the most useful details are the system voltage, the capacity, the expected discharge current, the operating temperature range and the physical space available. A pack that fits on paper can still fail in use if the discharge current, the temperature range or the terminal layout does not match the application. That is why this site asks buyers to confirm specifications per model, rather than selecting from a generic table.
A practical DOD checklist
Before choosing a home pack size, list the overnight load in energy terms, decide the intended depth of discharge for normal use, and convert the headline stored-energy figures of the candidate packs to usable energy at that depth. Then compare the usable figures with the overnight load, allowing a margin for inverter losses and for days when the load is higher than usual. That checklist prevents the most common sizing mistake, which is comparing headline figures without converting them to usable energy at a stated depth of discharge. The checklist also helps when comparing quotations, because a quotation that gives a headline figure without a depth-of-discharge limit cannot be compared with one that gives a usable figure at a stated limit.
Nominal voltage is the working voltage used to describe a pack, while charge voltage and cut-off voltage are separate limits. A 12.8 V pack, a 25.6 V pack and a 51.2 V pack belong to different systems and are not interchangeable, even when their capacities look similar. Buyers should confirm the system voltage, the charge voltage and the cut-off voltage for the exact model, and should check that the existing charger or inverter settings match those limits before ordering.
What this article does not do
This article does not recommend a depth of discharge for a particular house, because that recommendation needs the load pattern, the solar input and the cost considerations for that house. It does not give a cycle-life figure for the range, because cycle figures are stated per model with their conditions. It does not state a selling figure, because this site does not list fixed selling figures. Those limits are stated openly, so a reader does not mistake a general depth-of-discharge discussion for a personal sizing recommendation.
Quotations are confirmed per order. Minimum order quantity and lead time are unavailable on this site, so they are not stated as company policy and must be confirmed per model in the enquiry. This site does not list fixed selling figures, because a figure depends on the model, the quantity and the order terms. A quotation should list the model, the quantity and the specification confirmed for that model, so the buyer and the manufacturer are working from the same description.
Enquiry checklist
Before sending an enquiry, note the voltage, capacity, quantity, application and any required certification document. State whether the pack will be used indoors or outdoors, and whether a display or a particular terminal type is needed. Minimum order quantity and lead time are unavailable on this site and are confirmed per model in the enquiry. Quotations are confirmed per order.
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Frequently asked questions
How do I get a quotation?
Send an enquiry with the voltage, capacity and quantity you need, plus the application. Quotations are confirmed per order, and specifications are confirmed per model before payment. This site does not list fixed selling figures.
What certification documents can you provide?
ISO 9001 is stated by the company. Certificates are available upon request. If a buyer needs a certificate for a specific model, ask for it in the enquiry and name the model, so the correct document can be checked.
Are the specifications on this page valid for every model?
No. Specifications are shown per model and must not be read across the whole range. Where a value is not listed for a model, the page says to confirm per model rather than filling in a generic figure.