How long a 12V battery powers an inverter-connected load depends on battery capacity, the connected load’s wattage, and inverter efficiency losses. A 100Ah 12V battery typically runs a 100W load for roughly 8-10 hours through an inverter, accounting for conversion losses.
12V Battery Runtime Estimates
| Battery Capacity | 100W Load | 300W Load |
|---|---|---|
| 50Ah | ~4-5 hours | ~1.3-1.7 hours |
| 100Ah | ~8-10 hours | ~2.7-3.3 hours |
| 200Ah | ~16-20 hours | ~5.3-6.7 hours |
The Runtime Formula
Runtime (hours) = (Battery Ah × Battery Voltage × Depth of Discharge) ÷ (Load Watts ÷ Inverter Efficiency) — accounting for both how deeply you can safely discharge the battery and the inverter’s conversion losses (typically 85-95% efficient).
The Peukert Effect
Batteries deliver less total capacity at higher discharge rates than their rated Ah suggests — this “Peukert effect” means heavy loads drain a battery faster than simple math predicts, especially with lead-acid chemistry.
Lithium vs. Lead-Acid Depth of Discharge
Lithium (LiFePO4) batteries can be safely discharged to 80-100% of capacity, while lead-acid batteries should generally not exceed 50% discharge to preserve lifespan — this effectively halves usable capacity for lead-acid.
Inverter Efficiency Losses
Even a good inverter loses 5-15% of power as heat during DC-to-AC conversion — factor this into runtime calculations rather than assuming 100% efficiency.
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Frequently Asked Questions
How long will a 100Ah battery run a 100W load through an inverter?
Roughly 8-10 hours, accounting for inverter efficiency losses.
What is the Peukert effect?
A phenomenon where batteries deliver less capacity at higher discharge rates than their rated Ah suggests.
Can I discharge a lithium battery further than a lead-acid battery?
Yes — lithium can go to 80-100% discharge versus 50% for lead-acid.
How much power does an inverter waste?
Typically 5-15% is lost as heat during conversion.
Does battery voltage affect runtime calculations?
Yes — it’s part of the runtime formula alongside Ah, DoD, and load.
Why does my battery drain faster than calculated?
The Peukert effect and inverter losses both reduce actual runtime below simple math estimates.
What size battery do I need for a specific load?
Calculate using the runtime formula, then add a safety margin for real-world losses.
Summing Up
Battery capacity, depth of discharge, and inverter efficiency all affect real-world runtime. For home solar power solutions, call (855) 427-0058 or visit us.solarpanelsnetwork.com.
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