Solar Battery Recharge Time Calculator

Estimate how long a solar panel will take to recharge a 12V battery from a given depth of discharge.

Common questions

How long does a solar panel take to recharge a gate opener battery?: A 20W panel in full sun replaces about 1 Ah per hour of peak sun. A fully drained 7Ah battery needs ~7 hours of good sun to top up.
Why is my battery not fully recharging even in summer?: Common causes: undersized panel, shaded panel, dirty panel, undersized wire causing voltage drop, or a failing charge controller.
Does a bigger battery take longer to recharge?: Yes — proportionally. Doubling battery Ah roughly doubles the recharge time from the same panel.