Wh to mAh Converter

Converting watt-hours (Wh) to milliampere-hours (mAh) is critical for battery specification verification, cross-voltage capacity comparisons, regulatory compliance documentation, and charge controller sizing. While Wh provides universal energy measurement independent of voltage, mAh relates directly to current flow and charging systems, making the conversion essential where the relationship $E = Q \times V$ (energy equals charge times voltage) requires voltage knowledge. The conversion mAh = (Wh × 1,000) / V demonstrates voltage dependency, with identical Wh ratings producing dramatically different mAh values at different voltages requiring careful specification review.

Energy to Charge Capacity and Voltage Consideration: Watt-hours measure electrical energy (total work battery can perform), while milliampere-hours measure electric charge (quantity of electrons moved), related through voltage where mAh = (Wh × 1,000) / V. A 56 Wh battery at 11.4V contains 4,912 mAh, but same energy at 3.7V yields 15,135 mAh—different capacity values but identical energy storage. This explains why datasheets must specify both Wh and voltage or both mAh and voltage; specification listing only "5,000 mAh" is incomplete, representing either 18.5 Wh at 3.7V or 57 Wh at 11.4V with dramatically different energy capacities.

Multi-Cell Configuration and Series-Parallel Analysis: Multi-cell battery packs connect cells in series, parallel, or series-parallel combinations to achieve desired voltage and capacity, requiring pack total voltage for conversion not individual cell voltage. A 2S2P pack with 2,500 mAh 3.7V cells yields 5,000 mAh at 7.4V total (parallel doubles capacity, series doubles voltage), equaling 37 Wh. Electric vehicle and e-bike batteries use high-voltage packs (36V, 48V, 52V) reducing current for same power, minimizing conductor losses—500 Wh at 48V contains 10,417 mAh while same energy at 36V requires 13,889 mAh capacity.

Charger Sizing and CC/CV Protocol: Battery chargers specified by output current and voltage require Wh to mAh conversion for determining charging current and time where t = mAh / (mA × efficiency). A 98 Wh battery at 14.4V (6,806 mAh) with 2A charger theoretically charges in 3.4 hours, actually 3.8 hours with 90% efficiency. Lithium-ion charging follows constant current/constant voltage (CC/CV) protocol: initial 0.5C-1C constant current until 4.2V per cell, then constant voltage with current taper. The CC phase delivers 70-80% capacity, CV completes remaining 20-30%, with total time exceeding simple calculation due to taper.

Battery Chemistry Comparison: Lithium vs Lead-Acid: Different battery chemistries exhibit distinct voltage characteristics and depth-of-discharge limitations affecting capacity calculations. Lithium batteries tolerate 80-90% DOD regularly with 3000 cycles at 80% DOD, while lead-acid degrades rapidly beyond 50% DOD limiting regular use. A device requiring 50Wh runtime needs 100Wh lithium battery (50Wh / 0.8 = 62.5Wh minimum) or 100Wh lead-acid (50Wh / 0.5 = 100Wh). Charging efficiency differs: lithium 95-98% (requiring 102-105Wh input per 100Wh restored), lead-acid 70-85% (needing 118-143Wh input), affecting thermal management requirements.

Standards Reference: Aviation regulations per IATA require Wh specifications for lithium battery transport as energy determines fire hazard severity (99 Wh limit for carry-on). Medical device regulations (IEC 60601, FDA 510(k)) require comprehensive documentation including Wh energy content, mAh capacity, cycle life testing, and safety certification (UL 2054, IEC 62133). IEC 61960 and IEC 62133 establish secondary battery testing and safety requirements ensuring consistent specifications across manufacturers.