Depth of discharge (DoD) is how much of a battery’s capacity you use before recharging, and battery manufacturers’ cycle-life charts show it has a big effect on how many cycles a battery lasts. Drain a 100Ah battery down to 20Ah left and you’ve used 80Ah, an 80% depth of discharge. DoD is the opposite of state of charge (SoC): 80% DoD = 20% SoC.
Depth of Discharge vs State of Charge
| State of charge | Depth of discharge |
|---|---|
| 100% (full) | 0% |
| 80% | 20% |
| 50% | 50% |
| 20% | 80% |
| 0% (empty) | 100% |
How DoD Affects Cycle Life
Shallower cycles mean less stress, so a battery usually lasts more cycles at 50% DoD than at 100%. The size of the effect depends on chemistry:
- Flooded and AGM lead-acid: very sensitive. Many makers suggest staying above 50% SoC for decent life. Regular deep discharges can cut life sharply.
- LiFePO4: much more tolerant. Datasheets commonly rate thousands of cycles at 80% DoD. Using 100% is allowed but shortens life somewhat.
Always use the manufacturer’s DoD vs cycles chart; numbers vary widely.
Usable Capacity: The Number That Matters
Usable kWh = nominal kWh × recommended DoD
| Battery | Nominal | Recommended DoD | Usable |
|---|---|---|---|
| 12V 100Ah AGM | 1.2 kWh | 50% | ~0.6 kWh |
| 12V 100Ah LiFePO4 | 1.28 kWh | 80-100% | ~1.0-1.28 kWh |
| Home battery (example 13.5 kWh usable) | listed as usable | set by maker | 13.5 kWh |
Home batteries often list usable capacity because the system already reserves some.
Lifetime Energy Throughput
A useful way to compare is total energy over the battery’s life:
Throughput ≈ usable kWh × rated cycles
A battery that is cheap but rated for few cycles can cost more per kWh delivered than a pricier LiFePO4.
How to Size a Bank Around DoD
- Add up daily use in Wh
- Add days of autonomy you want
- Divide by the DoD you’ll run at
Example: 2,000 Wh/day × 1 day ÷ 0.8 = 2,500 Wh, about two 12V 100Ah LiFePO4 batteries.
Tips to Extend Life
- Avoid sitting at 0% or 100% for long periods
- Keep LiFePO4 at moderate temperatures and don’t charge below freezing
- Use a shunt-based battery monitor for accurate SoC
- Set low-voltage cutoffs on inverters and loads
Monitoring DoD in Practice
Voltage alone is a poor guide for LiFePO4, because its voltage curve is very flat between about 20% and 90% SoC. A shunt-based monitor counts amp-hours in and out, which gives a much better DoD reading. Reset it to 100% at each full charge so small errors don’t build up over weeks.
Depth of Discharge Formula
DoD (%) = energy or amp-hours removed ÷ rated capacity × 100
Illustrative examples:
| Battery | Removed | DoD | SoC left |
|---|---|---|---|
| 12.8V 100Ah | 30Ah | 30% | 70% |
| 12.8V 200Ah | 150Ah | 75% | 25% |
| 10 kWh home battery | 6 kWh | 60% | 40% |
| 1,024Wh power station | 512Wh | 50% | 50% |
Use the same units on both sides: amp-hours with amp-hours, or watt-hours with watt-hours. See amp-hours vs watt-hours.
Depth of Discharge Calculation for a Real Day
Illustrative inputs: a van uses 60Wh an hour overnight for 10 hours from a 12.8V 200Ah (2,560Wh) LiFePO4 bank.
| Step | Math | Result |
|---|---|---|
| Energy used | 60 × 10 | 600Wh |
| Add 10% conversion loss | 600 ÷ 0.9 | about 667Wh |
| DoD | 667 ÷ 2,560 | about 26% |
| SoC at sunrise | 100 − 26 | about 74% |
A 26% nightly cycle is gentle on the battery and leaves a reserve for a cloudy day.
How to Read a DoD vs Cycle Life Chart
Battery datasheets often show a curve or table of cycles against DoD. When you compare two of them, check three things:
- The DoD used for the headline number. A rating “at 80% DoD” isn’t directly comparable to one “at 100% DoD.”
- The end-of-life definition. Most ratings count cycles until capacity falls to 70% or 80% of new, not until the battery stops working.
- Test conditions. Temperature and charge and discharge rates, often around 25°C and 0.2–0.5C, affect the result.
A battery at “end of life” by datasheet definition still works. It just holds less, such as 80Ah from a battery that started at 100Ah.
Depth of Discharge of Lead-Acid vs Lithium
| Flooded / AGM lead-acid | LiFePO4 | |
|---|---|---|
| Common everyday DoD target | about 50% | about 80%, with 100% allowed |
| Effect of sitting partly charged | Sulfation builds up | Little effect at moderate SoC |
| Needs regular full charge? | Yes | Helpful for monitor calibration and cell balancing |
| Voltage tells you SoC? | Reasonably, at rest | Poorly, because the curve is flat |
Lifetime Throughput, Worked Out
Illustrative inputs only:
| AGM 12V 100Ah | LiFePO4 12.8V 100Ah | |
|---|---|---|
| Usable per cycle | 0.6 kWh (50% DoD) | 1.02 kWh (80% DoD) |
| Rated cycles at that DoD (illustrative) | 500 | 4,000 |
| Lifetime throughput | 300 kWh | about 4,100 kWh |
| Price (illustrative) | $200 | $300 |
| Cost per kWh delivered | about $0.67 | about $0.07 |
The cheaper battery up front can cost several times more per kWh delivered. Run the same math with the real datasheet numbers and prices for the batteries you’re comparing. See LiFePO4 vs lithium ion.
Equivalent Full Cycles
Real batteries rarely cycle neatly from full to empty. Battery monitors and many warranties count equivalent full cycles: total energy discharged divided by capacity. Illustrative: five days at 20% DoD each add up to one equivalent full cycle (5 × 20% = 100%). That’s why throughput in kWh is a fair way to compare batteries that are used differently.
Home Batteries and Reserve Settings
Home batteries usually list usable capacity and let you set a backup reserve, a share of the battery held back for outages. Illustrative: a 13.5 kWh usable battery with a 20% reserve has about 10.8 kWh available for daily self-consumption, while 2.7 kWh stays ready for an outage. A higher reserve means more outage protection and shallower daily cycles. See home battery backup for power outages.
Controlling DoD With Cutoff Settings
You set the maximum DoD in practice with the settings on your equipment:
| Setting | Where | What it does |
|---|---|---|
| Low-SoC shutdown | Battery monitor relay, ESS or GX settings | Stops discharge at a chosen SoC, such as 20% |
| Inverter low-voltage cutoff | Inverter settings | Shuts down at a set battery voltage |
| Backup reserve | Home battery app | Holds back a share for outages |
| Load disconnect | Charge controller load output or a relay | Drops DC loads at a set voltage |
SoC-based limits from a shunt are more accurate than voltage limits for LiFePO4, because its voltage stays nearly flat until it’s almost empty.
Temperature and Usable Capacity
Cold reduces how much capacity a battery can deliver, and most LiFePO4 datasheets block charging below about 0°C (32°F) unless the battery has heaters. Heat speeds up long-term aging. Keeping batteries at moderate room temperatures helps them deliver their rated cycles.
FAQ
What is a good depth of discharge?
For LiFePO4, 80% is a common daily target. For lead-acid, around 50%.
Is 100% DoD bad for LiFePO4?
Not harmful occasionally, but frequent full cycles reduce total cycle count.
Does DoD affect warranty?
Some warranties are based on years, cycles or total throughput. Read the terms.
What is the depth of discharge of a lithium-ion battery?
LiFePO4 datasheets often allow 80–100% DoD. Home batteries list usable capacity after their own reserve.
What is the depth of discharge of a lead-acid battery?
About 50% is a common everyday target for good cycle life.
How do I calculate depth of discharge?
Divide the energy or amp-hours used by rated capacity. 40Ah out of 100Ah is 40% DoD.
Sources: U.S. Department of Energy, “How Does Electricity Work?”; manufacturer battery datasheets; manufacturer battery warranty terms. Accessed Oct 2026.
Related: LiTime 12V 50Ah LiFePO4 Battery Review, EcoFlow Delta 3 Max Storage and Maintenance