Battery Capacity Ah to Wh Converter
Convert battery capacity metrics between Amp-hours (Ah) and Watt-hours (Wh) using nominal pack voltage. Fast, transparent calculator.
Parameters
Nominal voltage of cell stack or module
Estimated Outputs
A 1.28 kWh pack can power a 100W load for approximately 11.5 hours at 90% system efficiency.
Why nominal voltage matters
Two batteries with identical 100 Ah capacities can hold very different amounts of total energy. A 100 Ah 12V pack holds 1.2 kWh, whereas a 100 Ah 48V pack holds 4.8 kWh. Total energy capacity is the correct index for comparisons.
Mathematical Formulas
The conversion between electric charge capacity (Ah) and total energy capacity (Wh) is direct, based on Ohm's law:
Worked Engineering Example
Consider converting a deep-cycle marine battery rated at 100 Ah with 12.8V nominal voltage:
Step 1: Apply the Ah-to-Wh formula:
Step 2: Convert Wh to kWh:
This means a 12.8V 100 Ah battery stores 1,280 Wh of total chemical energy.
Frequently Asked Questions
What is the difference between Ah and Wh?
Amp-hours (Ah) measure electric charge capacity (the volume of electrons moving past a point). Watt-hours (Wh) measure total electric energy capacity (the volume of electrons multiplied by the electrical force, or voltage). Wh is the actual measurement of energy potential.
What voltage value should I use for nominal voltage?
Always use the average nominal voltage of the pack rather than peak charge or low discharge cut-off voltages. For example, a single LiFePO4 cell is nominal 3.2V (peak 3.65V, cut-off 2.5V). For a 4S system, nominal is 12.8V.
Why is capacity sometimes measured in Ah instead of Wh?
Historically, lead-acid batteries were standardized around 6V or 12V outputs, making Amp-hours a convenient shortcut comparison. However, with modern multi-voltage lithium architectures (12V, 24V, 48V, 400V, 800V), Watt-hours are required for safe comparison.
How do temperature effects impact Wh capacity?
Lower temperatures reduce chemical kinetics inside cells, which increases internal resistance and drops the cell's output voltage curve during discharge. Since Wh = Ah × V, this lower voltage drop directly translates to fewer total Watt-hours delivered.
How do I compare a 12V 200Ah battery with a 48V 100Ah battery?
Convert both to Wh: 12V × 200Ah = 2,400 Wh. 48V × 100Ah = 4,800 Wh. The 48V battery stores twice the energy despite having half the Ah rating. Always compare in Wh for fair comparison.
Can I use Ah to calculate runtime?
Only if the load is specified in amps. If the load is in watts (the more common case), convert to Wh first, then divide by load watts. Formula: Runtime (hours) = (Ah × V × DoD) / (Load W / Efficiency).
What is the relationship between Ah, Wh, and kWh?
Ah × Voltage = Wh. Wh / 1000 = kWh. For example, a 200Ah battery at 51.2V = 10,240 Wh = 10.24 kWh. kWh is simply Wh expressed in thousands for large systems.
Why do some batteries list only Ah and others only Wh?
Ah is traditional for lead-acid and some lithium manufacturers. Wh is increasingly preferred because it directly represents energy content. Always check if the stated Ah is at the pack's nominal voltage before comparing.
Does Ah capacity change with discharge rate?
Yes. Higher discharge rates reduce usable Ah due to internal resistance losses. This is especially pronounced in lead-acid (Peukert effect). A 100Ah lead-acid battery may deliver only 60Ah at 1C rate. LFP is less affected but still shows some capacity reduction at high C-rates.
How does DoD affect the Ah vs Wh comparison?
DoD limits reduce usable capacity in both Ah and Wh equally. A 100Ah battery at 80% DoD provides 80Ah usable, or (80Ah × V) Wh usable. The conversion between Ah and Wh remains valid regardless of DoD — DoD simply scales both proportionally.
Is Wh the best metric for comparing all batteries?
Wh is the best metric for comparing total energy content. However, for applications requiring high current, also consider max continuous discharge (A) and C-rate. Two batteries with the same Wh may have very different current delivery capabilities.
What Is Battery Capacity Ah to Wh Converter?
Why This Calculation Matters
→ Comparing batteries by Ah alone is misleading — a 100Ah 12V battery holds 3× less energy than a 100Ah 48V battery.
→ Load calculations require Wh, not Ah — a 500W load runs for 2.4 hours on 1,200 Wh but you need the correct unit.
→ Batteries at different voltages cannot be compared by Ah — only Wh provides a fair energy comparison.
→ Solar and backup systems are designed in Wh/kWh — converting Ah to Wh is the first step in any sizing calculation.
→ Charger specifications often mix Ah and Wh ratings — confusion leads to undersized or oversized charging systems.
Practical Applications
Battery Comparison Shopping
Compare batteries of different voltages and chemistries on equal footing by converting to Wh.
System Sizing
Convert Ah ratings to Wh for load-based energy storage sizing calculations.
Solar Design
Convert battery Ah ratings to Wh to match against daily solar production and consumption.
Runtime Estimation
Convert Ah to Wh to calculate how long a battery can sustain a given wattage load.
EV Range Calculation
Convert pack capacity from Ah to Wh for range estimation and energy consumption analysis.
Why Trust These Calculations?
The conversion formulas (Wh = Ah × V, Ah = Wh / V) are fundamental electrical relationships. All calculations are transparent and use standard SI units.
View our full methodology →Runtime Calculator
Estimate backup hours given a W load profile.
C-Rate Calculator
Analyze battery load speed parameters.
Battery Sizing Tool
Size packs from daily electrical draw.
Solar Battery Sizing
Size solar battery banks from daily consumption.
Battery Pack Calculator
Design series/parallel cell configurations.
References & Further Reading
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