Home › Power stations & batteries
Battery bank runtime calculator
How long will a 100Ah (or any) battery run your load? Accounts for chemistry, usable depth of discharge, inverter losses and the Peukert effect.
Results
| Estimated runtime | 10 h 11 min |
|---|---|
| Runtime ignoring Peukert | 10.37 hours |
| Battery current | 8.7 A |
| Usable energy | 1,152 Wh |
| Depth of discharge used | 90 % |
- The Peukert adjustment uses the battery's 20-hour rating. Lithium is barely affected, but lead-acid delivers noticeably less at high loads.
About this calculator
"How long will a 100Ah battery last?" depends mostly on chemistry. A 100 Ah LiFePO4 battery can deliver almost all of its rated energy. A 100 Ah AGM battery should only be taken down to about half if you want it to last more than a couple of hundred cycles. So the same "100 Ah" label can mean roughly twice the usable runtime.
This calculator applies the right usable depth of discharge for each chemistry and includes inverter losses for AC loads. It also uses Peukert's law, which explains why lead-acid batteries deliver less than their label when you pull current quickly.
How to use it
- Enter the battery's amp-hour rating and nominal voltage. For a bank, use the totals from the series/parallel calculator.
- Pick the chemistry. The usable depth of discharge fills in automatically, or you can override it.
- Enter your load in watts and whether it runs on AC (through an inverter) or DC.
- Compare the Peukert-adjusted runtime with the simple estimate. The gap shows how much discharge rate matters for your setup.
The formula
Battery current I = load W ÷ inverter efficiency ÷ nominal volts.
Peukert runtime t = H × (C ÷ (I × H))k, where C is rated Ah, H is the rating period (20 h) and k is the Peukert exponent (≈1.03 for LiFePO4, 1.1-1.25 for lead-acid).
Usable runtime = t × allowed depth of discharge.
Worked example (default values)
Inputs
| Battery capacity | 100 Ah |
|---|---|
| Nominal voltage | 12.8 V |
| Chemistry | LiFePO4 |
| Depth of discharge you'll allow (0 = chemistry default) | 0 % |
| Load | 100 W |
| Load type | AC through an inverter |
| Inverter efficiency (AC only) | 90 % |
Results
| Estimated runtime | 10 h 11 min |
|---|---|
| Runtime ignoring Peukert | 10.37 hours |
| Battery current | 8.7 A |
| Usable energy | 1,152 Wh |
| Depth of discharge used | 90 % |
Tips and common mistakes
Planning values used: usable depth of discharge is 90% for LiFePO4, 85% for NMC and 50% for AGM, gel and flooded lead-acid. Peukert exponents are typical mid-range values. Your battery's datasheet may list a specific one.
Cold matters. Lead-acid can lose 20-40% of its capacity near freezing. Most LiFePO4 batteries must not be charged below 32 °F (0 °C) unless they have built-in heating, though they can still discharge.
Frequently asked questions
How long will a 100Ah lithium battery run a 100W load?
Through an inverter, about 10 hours: 1,280 Wh × 90% usable ÷ about 111 W drawn from the battery. On DC with no inverter, it's about 11.5 hours.
How long will a 100Ah AGM battery last?
At 100 W AC, roughly 5 hours if you stop at 50% charge to protect its life (a 12 V, 100 Ah AGM holds 1,200 Wh, and only about 600 Wh of that is for regular use). Pushing it to 80% gets more runtime per cycle but far fewer cycles over its lifetime.
What is Peukert's law?
It describes how a battery's effective capacity shrinks as discharge current rises. It's significant for lead-acid and small for lithium.
Related calculators
- Amp-hours to watt-hours converter
Convert battery amp-hours (Ah) to watt-hours (Wh) and back for 12 V, 12.8 V LiFePO4, 24 V, 48 V and single lithium cells, with nominal voltage guidance.
- Battery bank series & parallel calculator
Work out the voltage, amp-hours and total energy of a battery bank wired in series, parallel or series-parallel, with wiring tips for matched batteries.
- Inverter size calculator
Size a power inverter from your appliance list: continuous watts, motor start-up surge, the next standard size and DC current from a 12, 24 or 48 V battery.
- Solar panel size calculator
Turn daily energy use into the solar array watts and number of panels you need, using peak sun hours and realistic losses. For RVs, vans, cabins and power stations.
More power stations & batteries calculators
- Battery charging time calculator
- Battery voltage chart and state-of-charge calculator
- CPAP battery runtime calculator
- Portable power station runtime calculator
- What size power station do I need?
Off-grid solar sizing, step by step
- Rough out the whole system · Off-grid solar system calculator
- Size the inverter from your loads · Inverter size calculator
- Plan the battery bank · Battery bank series & parallel calculator
- Check battery runtime (you are here)
- Size the solar array · Solar panel size calculator
- Check panel string voltage · Solar string voltage calculator (series & parallel)
- Choose the charge controller · Solar charge controller size calculator
- Size the DC cables · DC wire size calculator (12 V, 24 V, 48 V)
- Pick the fuses · DC fuse & breaker size calculator
Estimates for planning only, based on the assumptions shown. Real-world performance varies with equipment, temperature and installation. Updated October 19, 2026. See our methodology.