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What Is Depth of Discharge in a Battery?

Depth of discharge, usually written DoD, is the share of a battery’s capacity that has been used in a discharge. If a battery starts full and gives back half of its rated amp-hours, it has a depth of discharge of 50%. The Victron BMV-712 Smart manual we opened does not use the phrase “depth of discharge.” It uses the related setting called the “discharge floor,” along with state of charge and time-to-go readings. This article explains depth of discharge through those terms, because they are what a battery monitor actually shows.

Quick answer

• Depth of discharge is the part of a battery’s capacity that has been used, expressed as a percentage.
• State of charge is the part still available. As a simple approximation, 80% state of charge means 20% depth of discharge.
• The Victron BMV-712 Smart sets its discharge floor to 50% by default and tells users to set lead-acid batteries to 50% and lithium batteries lower.
• Time-to-go is calculated until the discharge floor is reached, so it changes with the load.

The simple meaning

Think of a battery as a tank with a fixed capacity in amp-hours (Ah). Depth of discharge tells you how much of that tank has been emptied. A 100 Ah battery that has supplied 50 Ah since it was full is at 50% depth of discharge. That arithmetic is an example, not a rating for any battery. The number changes as the battery is charged and discharged again.

The same idea appears in a battery monitor as state of charge, which is the amount left. Depth of discharge and state of charge add up to 100%. This is a simplification. The Victron manual says its state of charge figure is compensated for Peukert efficiency and charge efficiency, so a battery monitor’s reading is not a plain subtraction of Ah drawn from a fixed total. The manual also states that the state of charge is “the best way to monitor the battery.”

What the Victron manual says about the discharge floor

The discharge floor is the setting closest to depth of discharge in the BMV-712 Smart. The manual describes it this way: the “Discharge floor” parameter “is used in the ‘time remaining’ calculation.” The battery monitor works out how long it will take to reach the set discharge floor. The same setting also sets the defaults for the state of charge alarm.

The manual gives three values that matter for the setting. The default is 50%. The range is 0 to 99%, in 1% steps. For guidance by chemistry, it says: “For lead-acid batteries set this to 50% and for lithium set it lower.” It does not give a single lithium number in the chapter we read, so this article does not supply one.

The chapter also notes that the setting only appears in the VictronConnect app. When the battery monitor is read through the head unit, the manual points to the low state of charge relay setting instead. That relay, according to the manual, closes when the state of charge falls below the discharge floor setting, and opens again when the state of charge rises above the clear state of charge relay setting.

Why time-to-go is not the same as depth of discharge

Time-to-go is the other reading people see with the discharge floor. The Victron operation chapter describes it as “the actual time left until the battery is discharged to the set ‘discharge floor’.” It is an estimate of how long the present load can run before that floor is reached. The chapter adds that if the load fluctuates heavily, the reading should be used “as a guideline only,” and that the state of charge readout is recommended for accurate monitoring.

In practice, this means a short time-to-go number can come from a short burst of high current, not from a battery that is deeply discharged. When the load changes often, read the state of charge percentage. It tells you more about how much of the battery has been used than a single time estimate does.

How depth of discharge connects to capacity

Depth of discharge is a percentage, so it depends on the capacity it is measured against. The Victron battery capacity chapter explains that capacity “is expressed in Amp hour (Ah) and indicates how much current a battery can supply over time.” Its example is a 100 Ah battery discharged at a steady 5 A, which runs flat in 20 hours.

The same chapter adds that available capacity falls as the discharge gets faster. It says that “the faster the rate of discharge, the less capacity will be available.” The manual gives an example in which a 100 Ah battery discharged over two hours may give only about 56 Ah. For that reason, a fixed amp-hour figure does not always tell you the exact percentage used in a fast discharge.

The BMV-712 handles this with the Peukert exponent, which can be set from 1.00 to 1.50. The all-features chapter says that if the exponent is unknown, it should be set to 1.25 for lead-acid batteries and 1.01 for lithium batteries. A value of 1.00 turns off the Peukert compensation. The manual also calls the exponent “no more than a rough approximation of reality.”

A practical reading order

1. Confirm the battery capacity setting in amp-hours, because every percentage depends on it.
2. Check the discharge floor for your battery chemistry. The Victron manual’s default of 50% is the lead-acid value.
3. Read the state of charge percentage as the main figure. Use time-to-go only as a rough guide when the load is steady.
4. Note that the displayed percentage is an estimate that the monitor corrects over time, not a laboratory measurement.

Working on battery systems can involve high currents at the terminals. The Victron manual has a separate battery safety section, which this article does not summarize. Read it before any installation or service work, and do not rely on this page for safety instructions.

For meter basics before you check any battery, see How Do You Use a Multimeter Step by Step? A voltage reading alone does not give depth of discharge, but it helps you compare a battery with the state of charge the monitor reports. For how voltage readings relate to a lithium battery, read How to Test a 12 Volt Lithium Battery With a Multimeter.

How we chose

This explainer covers one term and the settings that use it. We limited the sources to the Victron BMV-712 Smart manual because it is a manufacturer document for a named model. The article draws on three chapters of that manual: the discharge floor settings, the operation chapter on time-to-go, and the capacity and Peukert chapter. We did not add a general battery article to fill the length. The arithmetic examples in this article are illustrations, and the only numbers quoted as product figures come from the manual.

What we could not verify

The sources we opened do not define depth of discharge as a formal term, and they do not give a recommended depth of discharge for any battery chemistry beyond the 50% default and the word “lower” for lithium. They do not link depth of discharge to cycle life, so this article makes no claim about how DoD affects battery lifespan. We did not find a readable Victron or Renogy source with a lithium discharge floor number that we could quote in full.

FAQ

Is depth of discharge the same as state of charge?

No. They describe the same battery from opposite sides. Depth of discharge is the share used, and state of charge is the share still available. Add them and you get 100%, as a simple approximation. The Victron monitor’s state of charge is corrected for efficiency losses, so the two numbers may not sum exactly to 100% in every reading.

What does 50% discharge floor mean?

The Victron default of 50% means the battery monitor treats the battery as reaching its discharge floor once the state of charge falls to 50%. The setting is used for the time-to-go estimate and the low state of charge alarm defaults. It is a setting in the monitor, and the manual says lead-acid batteries use 50% while lithium batteries should use a lower value.

Why does the time-to-go number jump around?

The manual says the figure is a momentary readout. When the load changes heavily, it changes too. Use the state of charge reading for a steadier view of how much capacity is left.

Where do I change the discharge floor?

According to the all-features chapter, the discharge floor appears in the VictronConnect app. The head unit shows the low state of charge relay setting instead. The manual gives the default and range in the settings table we read.

Does a deeper discharge always damage a battery?

The Victron chapters we opened do not say that. They describe capacity, state of charge and time-to-go, but they do not give a cycle-life rule. This article therefore does not claim a damage threshold, and readers should check the battery supplier’s own specification for that.

Bottom line

Depth of discharge is the part of a battery’s capacity you have used. Read it as the inverse of state of charge, set the discharge floor for your battery chemistry, and rely on the state of charge percentage rather than a single time-to-go estimate when the load changes.

Sources

• Victron Energy, “Manual – BMV-712 Smart Battery Monitor” (online edition), chapter 7.2.3 “Discharge floor” and chapter 7.2.1 “Battery capacity” in “All features and settings,” https://www.victronenergy.com/media/pg/BMV-712_Smart/en/all-features-and-settings.html, opened 2026-10-27.
• Victron Energy, “Manual – BMV-712 Smart Battery Monitor,” chapter 5.1 “How does the battery monitor work?”, https://www.victronenergy.com/media/pg/BMV-712_Smart/en/operation.html, opened 2026-10-27.
• Victron Energy, “Manual – BMV-712 Smart Battery Monitor,” chapter 8 “Battery capacity and Peukert exponent”, https://www.victronenergy.com/media/pg/BMV-712_Smart/en/battery-capacity-and-peukert-exponent.html, opened 2026-10-27.