Convert volts and amps into real power. Check capacity, depth of discharge, and efficiency losses. Design pack configurations, then compare outcomes across scenarios fast.
Choose a mode or leave it on Auto to compute everything possible.
These examples show typical inputs and expected outputs.
| Scenario | Voltage | Current | Capacity | Efficiency | DoD | Load Power | Power | Energy | Runtime |
|---|---|---|---|---|---|---|---|---|---|
| DC load on 24V bank | 24 V | 10 A | 100 Ah | 92% | 80% | 200 W | 240 W | 2400 Wh | 8.83 h |
| 12V accessory system | 12 V | 15 A | 60 Ah | 90% | 70% | 150 W | 180 W | 720 Wh | 3.02 h |
| Pack builder (10s4p cells) | 37 V | 20 A | 12 Ah | 94% | 90% | 500 W | 740 W | 444 Wh | 0.75 h |
Battery power in watts describes the instantaneous demand on a pack. Use P = V × I for DC loads, and measure voltage under load because sag can reduce delivered power. For motor or inverter systems, capture average and surge values; a 300 W tool can briefly exceed 900 W at startup. Compare computed power to your device label, then add 10–20% margin for cabling and connector losses. For AC loads, use true power ratings, not just volt‑amps.
Capacity in amp‑hours depends on voltage, so energy in watt‑hours is the better sizing unit. Compute E = V × Ah using nominal pack voltage or a mid‑discharge value. Example: 24 V and 100 Ah equals 2400 Wh. Two 12 V batteries in series keep 100 Ah but double energy, while parallel strings keep voltage and increase Ah. This calculator shows both Wh and kWh for reporting. Energy units simplify comparisons across different pack voltages.
Not all stored energy is available. Depth of discharge limits protect cycle life, and system efficiency accounts for conversion losses. Usable energy is Eusable = E × DoD × efficiency. For lithium packs, 80–90% DoD is common; for lead acid, 50–60% improves longevity. Inverter and controller paths often run 85–95% depending on load and wiring. Adjust these fields to match your design standard. Higher currents amplify losses, so efficiency may drop.
Runtime is t = Eusable ÷ load power. Use average power over the duty cycle, not peak. If a fan draws 120 W for 30 minutes per hour, the average is 60 W. For current‑driven estimates, usable amp‑hours divided by load current gives a second check. Expect variation with temperature, battery age, and high discharge rates. Document assumptions with exported CSV or PDF when sharing results. When uncertain, log measurements and refine inputs iteratively.
Series and parallel design changes both voltage and current capability. Pack voltage is Vcell × Ns and capacity is Ahcell × Np. Continuous and peak C‑rates translate to current limits: Imax = Ahpack × C. Exceeding limits increases heating and voltage drop, reducing real runtime. Use the pack builder to verify that expected load current stays within continuous and peak thresholds, then iterate Ns/Np to meet power and safety targets.
Use the voltage you expect under load. Nominal voltage works for planning, but measured operating voltage improves power and runtime estimates, especially for high currents and long cables.
High discharge rates reduce effective capacity, and voltage sag triggers cutoffs sooner. Temperature, aging, and conservative depth‑of‑discharge settings also shorten usable runtime compared with a simple Ah/I calculation.
Set efficiency to reflect the conversion path. A DC load may be 95–99% including wiring, while an inverter plus controller chain is often 85–95% depending on load, quality, and installation.
Lithium packs commonly use 80–90% to balance life and usable energy. Lead‑acid systems often target 50–60% for better cycle life. If datasheets specify limits, follow those values.
No. Series increases voltage while amp‑hours stay the same, so energy rises. Parallel increases amp‑hours at the same voltage. Use watt‑hours to compare pack sizes consistently.
C‑rate converts to current limit: Imax equals capacity in Ah times C. Staying within continuous limits reduces heating and voltage drop. Peak limits are for short bursts and should not be treated as steady operation.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.