About the 100Ah Lithium Battery Runtime Calculator
A standard 100Ah lithium battery (especially Lithium Iron Phosphate, or LiFePO4) is the benchmark power source for camper vans, marine setups, RV house banks, off-grid cabins, and home emergency backups. However, calculating runtime isn't as simple as dividing capacity by device wattage. To get a realistic estimate, you must account for pack voltage, Depth of Discharge (DoD), inverter conversion loss, and intermittent duty cycles.
If you also plan on charging your battery setup with solar panels during the day, check out our companion Solar Battery Runtime Calculator to calculate net solar generation and solar-assisted runtimes.
Key Features of This Calculator
- Multi-Voltage Support: Seamlessly switch between standard 12V, true LiFePO4 nominals (12.8V, 25.6V, 51.2V), or custom battery voltages.
- Series & Parallel Calculations: Calculate battery banks consisting of multiple 100Ah units wired in series (increasing voltage) or parallel (increasing capacity).
- Strict AC vs. DC Loss Separation: Inverter efficiency is applied exclusively to AC household appliances. Direct 12V/24V DC appliances bypass inverter losses entirely.
- Inverter Idle Draw Support: Factors in the continuous standby power drawn by pure sine wave inverters while switched on.
- Appliance Surge Warnings: Alerts you if starting motor surges exceed your inverter's continuous or surge wattage limits.
How the Calculation Works (Mathematical Engine)
This calculator relies on a multi-stage energy budget model:
Step 1: Calculate Nominal & Usable Battery Bank Energy
Nominal Energy (Wh) = [Single Battery Voltage (V) × Series Count] × [Single Capacity (Ah) × Parallel Count]Usable Energy (Wh) = Nominal Energy (Wh) × (DoD % / 100) × (1 - Safety Reserve % / 100)
Step 2: Determine Battery-Side Power Demand (Watts)
AC Appliance Battery Demand (W) = [Appliance Watts × Qty × (Duty Cycle % / 100)] / (Inverter Efficiency % / 100)DC Appliance Battery Demand (W) = Appliance Watts × Qty × (Duty Cycle % / 100)Total Battery Demand (W) = ∑ Demand(AC) + ∑ Demand(DC) + Inverter Idle Watts (if AC active)
Step 3: Continuous Backup Duration
Estimated Continuous Runtime (Hours) = Usable Energy (Wh) / Total Battery Demand (W)
Illustrative 100Ah (12.8V / 1,280Wh) LiFePO4 Runtime Table
Assumptions: 12.8V 100Ah battery, 90% Depth of Discharge (1,152 Wh usable), 90% Inverter Efficiency on AC loads, 0% reserve buffer.
| Appliance | Rated Power | Supply | Duty Cycle | Effective Draw | Estimated Runtime |
|---|---|---|---|---|---|
| Smart Phone Charger | 15W | DC | 100% | 15W | ~76 hours 48 mins |
| 12V Wi-Fi 6 Router | 20W | DC | 100% | 20W | ~57 hours 36 mins |
| CPAP (No Heated Tube) | 30W | DC | 100% | 30W | ~38 hours 24 mins |
| 12V RV Compressor Fridge | 45W | DC | 35% | 15.75W | ~73 hours 8 mins |
| Work Laptop (AC Charger) | 65W | AC | 100% | 72.2W (inverter) | ~15 hours 57 mins |
| 50-inch LED Smart TV | 80W | AC | 100% | 88.9W (inverter) | ~12 hours 57 mins |
| Household Refrigerator | 150W | AC | 35% | 58.3W (inverter) | ~19 hours 45 mins |
| Microwave Oven | 1,000W | AC | 100% | 1,111W (inverter) | ~1 hour 2 mins |
Frequently Asked Questions (FAQ)
1. How long will a 100Ah lithium battery last?
On a 12.8V LiFePO4 battery running at 90% Depth of Discharge (1,152 usable Wh), runtime depends entirely on the connected wattage. For example, a 100W AC device using a 90% efficient inverter draws roughly 111W from the battery, yielding about 10 hours and 22 minutes of runtime.
2. How long will a 100Ah LiFePO4 battery run a 12V appliance?
Direct 12V DC loads bypass inverter losses. If your 12V appliance draws 60W (5 Amps at 12V), it will run for approximately 19 hours and 12 minutes on an 1,152Wh usable bank (1,152Wh / 60W = 19.2 hours).
3. How long can a 100Ah lithium battery power a refrigerator?
A typical 12V DC portable fridge (drawing 45W while active, cycling at a 35% duty cycle) uses an average of 15.75W. On a 100Ah lithium battery, it will run for approximately 73 hours (over 3 days). A larger 120V household refrigerator through an inverter typically runs for 18 to 22 hours.
4. Can a 100Ah lithium battery run a CPAP machine all night?
Yes, easily. A standard CPAP machine on a 12V DC adapter without heated humidification consumes 20W to 35W, running comfortably for 32 to 50 hours (several consecutive nights). With a heated humidifier running on AC via an inverter, consumption rises to 70W–100W, offering 10 to 14 hours of continuous backup.
5. How many watts can a 100Ah lithium battery supply?
Wattage delivery is determined by your battery's internal Battery Management System (BMS) continuous discharge rating. Most 12.8V 100Ah batteries have a 100A BMS, meaning they can safely supply a maximum continuous load of 1,280 Watts (12.8V × 100A = 1,280W).
6. Does inverter efficiency affect battery runtime?
Yes. DC-to-AC power inverters convert 12V/24V DC to 120V/230V AC with an efficiency of 85% to 94%. The remaining 6% to 15% is lost as heat. Inverters also draw a baseline idle current (quiescent power) simply staying turned on.
7. Can I run multiple appliances from a 100Ah lithium battery?
Yes. You can run multiple appliances simultaneously, provided their combined battery-side wattage does not exceed your battery's BMS discharge rate or your inverter's continuous output capacity.
8. What is the difference between 100Ah and 100Wh?
Amp-hours (Ah) measure electrical charge capacity, whereas Watt-hours (Wh) measure total energy. To calculate energy, multiply Amp-hours by voltage (Ah × V = Wh). A 12.8V 100Ah battery provides 1,280Wh of energy, whereas a 48V 100Ah battery holds 4,800Wh—nearly four times the energy despite having the same Ah rating.
9. How much usable energy does a 100Ah LiFePO4 battery have?
Unlike traditional lead-acid batteries (which should only be discharged to 50%), a 100Ah LiFePO4 battery can safely discharge 80% to 90% of its capacity without compromising cycle life. That equates to 1,024Wh to 1,152Wh of usable energy from a 12.8V pack.
10. Can solar panels extend the runtime of a lithium battery?
Yes. Connecting a solar array directly charges the battery while your appliances operate. If solar power matches or exceeds appliance demand, your battery won't discharge at all during peak sun hours. To model this interaction, use our Solar Battery Runtime Calculator.