12V Install Tools & Testers
Battery Charging Time Calculator
Estimate how long a charger takes to bring your battery from one charge level to another.
Enter your battery, how full it is now and how full you want it, and the charger's output current. This works for a mains charger, a DC-DC charger or the average current from solar. It's an estimate under simple assumptions, shown below. Everything is worked out in your browser. Nothing is saved or sent anywhere.
1. Your battery
Changing this resets the round-trip efficiency below to its default.
2. Your charger
The current into the battery. For solar, use the average over the day, not the panel's peak.
Victron gives 92% for LiFePO4 and 80% for an average lead-acid battery.
3. Results
How it was worked out
What this does and doesn't tell you
- This is an estimate. It assumes the charger delivers its full current the whole time. Real charging slows as the battery nears full, so the last part takes longer.
- Lead-acid batteries (AGM, gel, flooded) need a long absorption stage to reach full, and Victron notes their charging "becomes particularly inefficient" above about 80% state of charge. Expect a full charge to take noticeably longer than shown.
- Charge level is hard to read from voltage alone, especially for lithium. A battery monitor with a shunt gives a better figure. See Battery Management.
- The charger must support your battery's chemistry and the maker's charging specifications, including voltage, maximum current and temperature limits. Many lithium batteries won't charge below their minimum temperature.
- Any work on 240V AC wiring, including mains inlets and hard-wired chargers, must be done by a licensed electrician.
Sources for the default assumptions
- Round-trip efficiency (LiFePO4 92%, average lead-acid 80%) and the lead-acid efficiency note: Victron Energy, 12,8 Volt lithium iron phosphate batteries Smart datasheet.
Next steps
Choosing a charger? Size a DC-DC charger with the DC-DC Charger Size Calculator, or work out the mains charger current you need with the Charger & Inverter Sizing Calculator. To see how solar and driving cover your daily use, try the Solar & Charging Check.