Battery Charge Time Calculator
How long to charge your battery from an AC charger, DC-DC charger, or solar array. Chemistry-aware absorption phase and charge losses for LiFePO4, AGM, Gel, and lead-acid banks at 12V, 24V, or 48V.
Battery Charge Time Calculator
round-trip eff 95%
= 240 W charge power · 0.20C rate
Advanced settings
Charge Time
1011 Wh to add @ 240 W charger
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VoltPlan designs full electrical systems with automatic wire sizing, fuse placement, charger configurations, and solar.
Design Your SystemRecommended Charge Rates by Chemistry
Maximum and recommended charge currents as a fraction of nameplate capacity (C-rate). Higher is faster but trades cycle life. The calculator flags rates outside the recommended band.
| Chemistry | Recommended | Max | Absorption phase |
|---|---|---|---|
| LiFePO4 | 0.5C | 1.0C (BMS-dependent) | ~5% of bulk |
| AGM | 0.2C | 0.3C | ~20% of bulk |
| Gel | 0.2C | 0.3C | ~20% of bulk |
| Flooded lead-acid | 0.1–0.15C | 0.2C | ~25% of bulk |
Frequently Asked Questions
How long to charge a 100Ah LiFePO4 from 20% to 100%?
With 20A AC charger: 4–5 hours. With 50A DC-DC: ~2 hours. With 200W solar at 5 sun-hours/day: ~1.5 days. Use the calculator above for your specific charger and chemistry.
Bulk vs absorption phase?
Bulk = constant-current, fast. Absorption = constant-voltage, taper, finishes the last 5–25% depending on chemistry. LiFePO4 has very short absorption; lead-acid types need much longer.
What is the safest charge rate for LiFePO4?
0.5C is the comfortable default (50A on a 100Ah battery). Most BMSs cap at 1.0C. Always check the spec sheet — some cheaper drop-ins limit to 50A regardless of capacity.
Why does the calculator show charge losses?
Energy in > energy stored. LiFePO4 round-trip is ~95%; lead-acid ~80%. The calculator divides the energy to replace by the efficiency to give a realistic charge time.
How accurate is the solar sun-hours model?
Sun-hours is an industry-standard way to model average daily solar output. It is conservative — actual output varies with weather, panel angle, and shading. Use 4–5 sun-hours for temperate climates, 5–6 for sunny ones.
Can I parallel two chargers to charge faster?
Yes, as long as the total current stays within the battery and BMS limit. Two 30A chargers in parallel is equivalent to one 60A charger. Match the absorption voltage on both to avoid one finishing early.
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