100Ah battery runtime by load
These are CALCULATED ESTIMATES, not measured runtimes. Both columns use 12.8V, 100Ah, 90% usable DoD and a 10% reserve; AC also uses 92% efficiency. Values are rounded for planning.
| Constant load | Direct DC | AC through inverter | Ideal DC current at 12.8V |
|---|---|---|---|
| 10W | about 103.7 h | about 95.4 h | 0.8A |
| 20W | about 51.8 h | about 47.7 h | 1.6A |
| 50W | about 20.7 h | about 19.1 h | 3.9A |
| 100W | about 10.4 h | about 9.5 h | 7.8A |
| 200W | about 5.2 h | about 4.8 h | 15.6A |
| 300W | about 3.5 h | about 3.2 h | 23.4A |
| 500W | about 2.1 h | about 1.9 h | 39.1A |
| 800W | about 1.3 h | about 1.2 h | 62.5A |
| 1,000W | about 1.0 h | about 57 min | 78.1A |
What can a 100Ah LiFePO4 battery run?
A 100Ah battery can run many low- and medium-power devices, provided its voltage, BMS, wiring and power converter are compatible. The ranges below are planning inputs—not universal device specifications. Check the device label or, better, measure average power.
| Device scenario | Planning load | Estimated runtime | Important caveat |
|---|---|---|---|
| Wi-Fi router | 8–15W, direct DC | about 69–130 h | Adapter and voltage-converter losses vary. |
| Laptop | 30–65W, AC | about 15–32 h | Charging and CPU load change draw. |
| CPAP | 30–60W, AC | about 16–32 h | Heated humidifier settings can materially increase power; follow medical-device backup guidance. |
| Portable fridge | 35–60W while running, direct DC | about 17–30 h if constant | Compressor cycling, ambient temperature and startup current drive actual runtime. |
| TV | 40–100W, AC | about 9.5–24 h | Screen size and brightness matter. |
| Fan | 20–50W, AC | about 19–48 h | Speed setting changes power. |
| Starlink Mini | 20–40W typical, direct DC | about 26–52 h | Starlink publishes the power range; connection losses still vary. See the dedicated Starlink Mini runtime guide. |
| Desktop PC | 100–300W, AC | about 3.2–9.5 h | GPU and workload can cause large swings. |
| Small appliance | 500–1,000W, AC | about 57 min–1.9 h | Check BMS, inverter, surge, cable and fuse limits first. |
The Starlink Mini 20–40W figure is an OFFICIAL MANUFACTURER SPECIFICATION from Starlink support. All runtime values are PowerUseLab calculations with the assumptions stated above.
Direct DC vs AC through an inverter
Direct DC
Battery → compatible DC device or DC converter. The calculator does not apply inverter efficiency. A separate DC converter can still have losses; reduce the usable DoD or add reserve if you want to model them conservatively.
AC through an inverter
Battery → inverter → AC device. The calculator multiplies usable energy by the selected inverter/system efficiency. It does not separately add inverter standby draw, so include that draw in the load when material.
nominal Wh = voltage × Ah
usable Wh = nominal Wh × DoD × efficiency × (1 − reserve)
runtime hours = usable Wh ÷ load watts
High-load current and BMS limits
The energy calculation answers “for how long,” but it does not prove that a battery can safely supply the load. For DC, current ≈ watts ÷ voltage. A 1,000W load at 12.8V is about 78A before conversion losses; through a 92% efficient inverter, battery-side current is about 85A, before inverter idle draw. That 84.9A figure is a nominal-voltage estimate; for a roughly constant-power AC load, battery current can rise as battery voltage falls.
If the load is a trolling motor, runtime is usually clearer from measured amp draw. Use the trolling motor battery runtime calculator rather than copying a generic watt estimate.
What changes actual runtime?
Load behavior
Fridges cycle, computers vary with work, and motors surge. Average measured power is more useful than a maximum label alone.
Battery condition
Temperature, age, state of charge, cell balance and the BMS cutoff all affect energy delivered.
Conversion path
Inverter efficiency, standby draw, DC-converter loss, wiring resistance and voltage drop reduce output.
Operating limits
High current can trigger a BMS or inverter cutoff before the simple watt-hour estimate reaches zero.
100Ah is nominal capacity, not a universal usable amount
The 100Ah label is nominal charge capacity. This page’s 90% usable DoD is an editable planning choice, not a claim that every 100Ah LiFePO4 battery physically provides exactly 90Ah. The manufacturer’s specified operating limits should control. Holding a 10% planning reserve then leaves 81% of nominal energy before AC conversion loss.
LiFePO4 batteries commonly support deeper planned discharge than lead-acid batteries. Lead-acid effective capacity also changes more with discharge rate because of the Peukert effect. Equal nominal Ah therefore does not guarantee equal usable runtime.
Verified 100Ah LiFePO4 examples
This is a specifications reference, not a ranking or buying recommendation. The product values come from current official manufacturer pages or manuals; PowerUseLab has not independently measured these batteries. Runtime still uses the calculator assumptions, not manufacturer test claims.
| Battery | Published voltage | Capacity | Energy / basis | 100W AC estimate* | Published discharge/output rating | Published peak | Official source |
|---|---|---|---|---|---|---|---|
| LiTime 12V 100Ah LiFePO4 Lithium Deep Cycle BatteryGroup 31 Basic / Classic; no Bluetooth or self-heating | 12.8V | 100Ah | 1,280Wh OFFICIAL | 9.5 h CALCULATED | 100A continuous | 400A for 1 second | LiTime product page |
| Renogy 2-in-1 Smart PowerMax 1280Wh DC Portable Power Station / 12V 100Ah LiFePO4 BatterySKU DKITBT121B-H-NEW-US; battery specifications shown | 12.8V | 100Ah | 1,280Wh OFFICIAL | 9.5 h CALCULATED | 100A continuous | Not stated for the battery on cited page | Renogy product page |
| Epoch 12V 100Ah Eco Series LiFePO4 BatteryModel 12100-ECO | 12.8V | 100Ah | 1.28kWh OFFICIAL | 9.5 h CALCULATED | 100A continuous | 300A for 5 seconds | Epoch technical datasheet |
| Battle Born 100 Amp Hour 12 Volt Lithium BatteryModel BB10012 | 12V | 100Ah | 1,200Wh from 12V × 100Ah CALCULATED | 8.9 h CALCULATED | 100A continuous | 200A for 30 seconds | Battle Born product manual |
*100W AC runtime uses 90% DoD, 10% reserve and 92% efficiency. The manufacturer’s exact nominal-voltage convention matters: PowerUseLab does not silently convert a published “12V” specification to 12.8V. No independent test or owner-report evidence is used in this table.
Need a target runtime? Reverse-size the battery
This secondary estimate answers “I need X hours at Y watts—how much nominal capacity would I need?” It shares the voltage, power path and advanced assumptions from the main calculator.
—
required nominal Wh = load × hours ÷ [DoD × efficiency × (1 − reserve)]
required Ah = required nominal Wh ÷ voltage
This is an energy estimate, not compatibility approval. Round up and verify BMS, surge, wiring, charging and manufacturer limits.
Calculation methodology
PowerUseLab retains full precision in calculations and rounds only the display. The calculator treats direct DC as 100% at the inverter stage because no inverter is present; any separate DC-converter loss must be modeled by a more conservative input. AC applies the selected system efficiency once. The reserve is applied after DoD and conversion efficiency.
For the default AC 100W example: 1,280Wh × 0.90 × 0.92 × 0.90 ÷ 100W = 9.53856 hours. See the site-wide calculation methodology for broader formulas and limitations.
Frequently asked questions
How long will a 100Ah lithium battery last?
Divide planned usable watt-hours by average load watts. With this page’s defaults, a 12.8V 100Ah LiFePO4 battery provides about 1,037Wh to a direct-DC load or 954Wh to an AC load, so runtime ranges from days at low loads to under an hour near 1,000W AC.
How long will a 12V 100Ah battery last?
At exactly 12V, nominal energy is 1,200Wh. At 12.8V, common for LiFePO4, it is 1,280Wh. Use the manufacturer’s nominal voltage, then apply usable DoD, reserve and applicable conversion loss.
How many watts are in a 100Ah LiFePO4 battery?
Amp-hours are capacity, not watts. Multiply voltage × Ah to get watt-hours: 12.8V × 100Ah is about 1,280Wh nominal.
Can a 100Ah battery run a refrigerator?
Often, if voltage, startup surge, BMS and wiring are compatible. Use measured average energy over time because compressor cycling makes nameplate or running watts an incomplete runtime input.
Can a 100Ah battery run a 1,000W inverter load?
Energy alone does not decide. At 12.8V and 92% efficiency, 1,000W AC draws about 85A from the battery before inverter idle draw. The battery BMS, inverter, surge rating, wiring, fuse and installation must all support it.
How long will 100Ah last at 100W?
With the defaults on this page, about 10.4 hours on direct DC or 9.5 hours through a 92% efficient inverter.
Is a 100Ah LiFePO4 battery really 100Ah usable?
100Ah is the nominal rating. Usable capacity depends on the product’s specified discharge limits, temperature, age and cutoff behavior. The calculator’s 90% DoD is a planning assumption, not a universal physical rule.
Why is my actual runtime lower than the estimate?
Common causes include a fluctuating load, low starting state of charge, cold temperature, battery aging, inverter standby draw, conversion and wiring losses, voltage sag, or an early BMS or inverter cutoff.