You know the charger's output voltage is 5 volts, so you settle on amp hours for battery capacity and amps for charge rate. But you're unable to find the battery's voltage, which you need to convert milliamp hours to watt hours. You consider watt hours for battery capacity and watts for charge rate. Let's consider the following scenario where the units are mismatched.įirst, you need to decide which set of matching units you want to convert to. Example 3: Battery Capacity in Milliamp Hours, Charging Rate in Watts In this scenario, your estimated charge time is 8 hours. Example 2: Battery Capacity in Watt Hours, Charging Rate in Wattsīecause your units are again 'matching', to calculate charging time you again simply divide battery capacity by charging rate. Tip: You can estimate how much battery capacity you need by using the inverse of this formula: amps × hours = amp hours. In this scenario, your estimated charge time is 10 hours. To calculate charging time using this formula, you simply divide battery capacity by charging current. Example 1: Battery Capacity in Amp Hours, Charging Current in Amps The formula itself is simple, but taking into account all the possible conversions can get a little overwhelming.

amp hours = kilowatt hours ÷ volts × 1000.

kilowatt hours = amp hours × volts ÷ 1000.

milliamp hours = watt hours ÷ volts × 1000.

watt hours = milliamp hours × volts ÷ 1000.

Most of them link to our relevant conversion calculator. In these cases, you need to convert the units until you have a 'matching' pair - such as amp hours and amps, watt hours and watts, or milliamp hours and milliamps.įor reference, here are the formulas you need to convert between the most common units for battery capacity and charge rate. Or they may be given in milliamp hours and watts. Your battery capacity may be given in watt hours and your charge rate in amps. charge time = battery capacity (mAh) ÷ charge current (mA)Ĭharge time = battery capacity (Wh) ÷ charge rate (W)Īnd sometimes, your units are mismatched. So you may also see the formula written with different unit combinations. And your battery charger may tell you its power output in milliamps (mA) or watts (W) rather than amps. However, battery capacity can also be expressed in milliamp hours (mAh), watt hours (Wh) and kilowatt hours (kWh). So you'll often see this formula written with these units: charge time = battery capacity (Ah) ÷ charge current (A) Most often, your battery's capacity will be given in amp hours (Ah), and your charger's charge current will be given in amps (A). The easiest but least accurate way to estimate charge time is to divide battery capacity by charge current. Formula 1įormula: charge time = battery capacity ÷ charge current I start with the simplest and least accurate formula and end with the most complex but most accurate. 3 Battery Charging Time Calculation Formulasįor those interested in the underlying math, here are 3 formulas to for calculating battery charging time. Click 'Calculate Charge Time' to get your results. If your battery is dead, you'd enter 0.Ħ. For instance, if your battery is 20% charged, you'd enter the number 20.

Optional: Enter your battery state of charge as a percentage. Select your battery type from the list.ĥ. Depending on the combination of units you selected for your battery capacity and charge current, the calculator may ask you to input a voltage.Ĥ. If the calculator asks for it, enter your battery voltage or charge voltage. The unit options are milliamps (mA), amps (A), and watts (W).ģ. Enter your battery charger's charge current and select its units from the list. The unit options are milliamp hours (mAh), amp hours (Ah), watt hours (Wh), and kilowatt hours (kWh).Ģ. Enter your battery capacity and select its units from the list. Tip: If you’re solar charging your battery, you can estimate its charge time much more accurately with our solar battery charge time calculator.

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