⏱️ Battery Runtime Calculator¶
Estimate how long a battery will power a given load. Based on Amp-hour capacity, battery type, and load wattage.
Formula: Runtime (hours) = (Ah × DoD) ÷ (Watts ÷ 12V)
:material-help-circle: Frequently Asked Questions¶
How long can a car battery run accessories?¶
A typical 65Ah SLI battery running a 100W device (~8.3A) will last approximately 2.5 hours before reaching the safe discharge limit. AGM batteries can run longer (deeper discharge tolerance). Never discharge a car battery below 50% (SLI) or it may sustain permanent damage.
Can I use my car battery for camping power?¶
Yes, but with limitations. SLI batteries are designed for short, high-current bursts (starting), not deep discharge. For camping, consider a deep-cycle or AGM battery. Always carry a jump starter as backup.
What's the difference between SLI and deep cycle for running accessories?¶
SLI batteries should not be discharged below 70% (only 30% usable capacity). Deep cycle batteries can be discharged to 20% (80% usable). AGM is in between at ~50% usable. The calculator adjusts for battery type.
How do I convert watts to amps for 12V?¶
Amps = Watts ÷ Volts. For a 12V system: a 120W device draws 10A, a 60W device draws 5A, a 12W device draws 1A. The calculator does this automatically.
Will running accessories drain my starting ability?¶
Yes. If you run the battery below 12.0V (approximately 50% discharge), the vehicle may not start. Plan to stop using accessories when voltage drops below 12.2V, or run the engine periodically to recharge.
How do I recharge after running accessories?¶
Drive for at least 30 minutes at highway speeds, or use a smart battery charger. A deeply discharged battery may need 4-8 hours on a charger.
Related resources¶
- Reserve capacity testing — how RC is defined
- Battery model database — RC and capacity by model
- Battery technology guide — SLI, EFB and AGM duty cycles