Battery Charge Time Calculator — Solar Charging Hours
How long will your solar array take to charge your battery bank? Enter your bank size, chemistry, and array wattage — this calculator applies the chemistry charge-rate cap (0.5C for LiFePO4, 0.2C for lead-acid), controller efficiency (MPPT vs. PWM), and real-world peak sun hours to estimate charging time in hours and days.
Why chemistry and controller matter
Charge-rate cap: LiFePO4 batteries safely accept up to 0.5C (half their amp-hour rating in amps); lead-acid should stay near 0.2C. A big solar array can't force a small battery to charge faster — the calculator caps effective charge power at the chemistry limit. Controller efficiency: MPPT controllers convert roughly 95% of panel output into charging current; PWM units waste voltage headroom and deliver about 75%. Sun hours: panels only produce rated power at peak sun — most US locations average 4–5 peak sun hours per day, so a "6-hour" charge takes about 1.5 days of real weather.
Lead-acid banks also slow down during the absorption stage (the last ~20% takes disproportionately longer), so real lead-acid charge times run 10–20% longer than the estimate. Cold temperatures reduce charging speed for all chemistries.