It takes your battery size, depth of discharge, panel power, and efficiency. Then it shows the charging time in hours. The formula is: Charging Time (hours) = (Battery Wh × DoD) ÷ (Panel W × Efficiency) Let's break it down in plain English: Battery Wh is your battery energy in watt-hours. A Battery Charge Time Calculator is a smart online tool that helps you estimate how long it will take to fully charge your battery based on battery capacity (Ah, mAh, Wh), charger current (amps), charger power (watts), or solar panel output. Optional: If left blank, we'll use a default value of --- 50% DoD for lead acid batteries and 100% DoD for lithium batteries. This calculator is especially useful for people who use rechargeable batteries in devices like electric vehicles, power banks, or any electronic. Use our solar panel size calculator to find out what size solar panel you need to charge your battery in desired time.