dawnice · Free Engineering Tools

Free Battery Calculators: Size, Convert & Plan Your Energy Storage

Three free battery calculators for solar installers, B2B buyers and facility managers worldwide. Size your 48V / 51.2V LiFePO4 battery, convert watts to amps, and calculate runtime — no sign-up, no limits, built for projects across Europe, Africa, Central Asia and Asia.

Browse Calculators Get a Free Sizing
Battery Capacity Watts / Volts / Amps kWh ↔ Watts
Tool Library

Three Calculators, One Workflow

A complete solar battery calculator toolkit. Each tool solves one step of battery sizing — use them in sequence, or jump straight to the one you need.

Popular

Battery Capacity Calculator

Calculate total energy (kWh), usable energy at 80% DoD, runtime at a given load, and the required Ah for a target backup time. Supports 12V / 24V / 48V / 51.2V systems.

Best for: You know the battery Ah and voltage, and need to find kWh or how long it will run your load.
Open Calculator

Watts / Volts / Amps Converter

Convert watts to amps, amps to watts and volts to watts in real time. Enter any two values and the third updates instantly — with lookup tables for 120V, 240V and 48V / 51.2V systems.

Best for: You know the load watts and system voltage, and need to find current to size cables, breakers and inverters.
Open Calculator

kWh to Watts Converter

Convert watts to kWh and kWh to watts with time-based accuracy. Enter any two of power (W), time (h) or energy (kWh) — the third is calculated instantly. Includes kW ↔ watts lookup.

Best for: You know daily energy use (kWh) or battery capacity, and need to find the average watts or backup runtime.
Open Calculator
How to Use

3 Steps to Size Your Battery System

Follow this sequence to go from a load list to a correctly sized 48V / 51.2V LiFePO4 battery quote.

1

Calculate Capacity

List your loads in watts, add your target backup hours, and find the required kWh and Ah. Check usable energy at 80% DoD.

Use Capacity Calculator
2

Match Current & Cables

Convert your total load watts to amps at 48V or 51.2V. Use the result to spec cable gauge, breaker size and inverter rating.

Use Watts / Amps Converter
3

Verify Runtime

Cross-check: divide your battery kWh by the load watts to confirm real-world runtime. Adjust capacity if the hours fall short.

Use kWh / Watts Converter
Why It Matters

Why Use dawnice Battery Calculators?

Free & No Sign-up

All three tools are 100% free. No email, no account, no watermarks — just open and calculate.

48V / 51.2V Accurate

Built around real LiFePO4 architecture: 16-cell 51.2V nominal, 80% DoD, commercial-grade BMS limits.

Global Grid-Ready

Defaults cover stable European grids and the 8–12 hour backup windows common across Africa, Central Asia and parts of Asia.

Mobile Friendly

Every calculator works on phone, tablet and desktop. Use it on-site with a customer, no laptop needed.

Quick Guide

Battery Sizing in Plain English

Sizing a battery system comes down to three numbers: load in watts, backup time in hours, and battery capacity in kWh. The relationship is simple: kWh = watts × hours ÷ 1,000. A 1,500W load running for 8 hours needs 12 kWh of energy — before any safety margin. This is the core of every battery size calculation.

But watts alone do not tell the whole story. At 48V, that same 1,500W draws about 31 amps; at 12V it draws 125 amps. Higher voltage means lower current, thinner cables and less heat loss. This is why commercial and industrial systems almost always use 48V or 51.2V — and why our calculators default to those voltages.

Finally, remember that a battery’s rated kWh is not all usable. LiFePO4 chemistry is typically limited to 80% depth of discharge to protect cycle life. A 5.12 kWh pack delivers about 4.1 kWh of usable energy per cycle. Always add this margin when quoting a system — and when estimating battery run time, divide usable energy by the load, not the rated capacity.

For a complete walkthrough of energy units and how they drive solar + storage design, read our kWh to kW conversion guide. For battery fundamentals, see what Ah means on a battery.

FAQ

Battery Calculator FAQ

What size battery do I need for my solar system?
Start with your total daily load in watts and the hours of backup you need. Multiply watts by hours and divide by 1,000 to get kWh, then add a 20–25% margin for depth of discharge and inverter efficiency. For example, a 1,500W load needing 8 hours of backup requires about 12 kWh raw, or roughly 15 kWh usable — equivalent to three dawnice 5.12 kWh packs in parallel.
How do I calculate battery runtime?
Runtime (hours) = battery capacity (Wh) ÷ load (watts). A 5.12 kWh pack on an 800W load runs 5,120 ÷ 800 = 6.4 hours at 100% DoD, or about 5.1 hours at the recommended 80% DoD. Use the Battery Capacity Calculator for an instant result with DoD built in.
What is the difference between kWh and Ah?
Ah (amp-hours) measures capacity at a specific voltage; kWh (kilowatt-hours) measures total energy regardless of voltage. To convert: kWh = voltage × Ah ÷ 1,000. A 48V 100Ah battery stores 4.8 kWh; a 51.2V 100Ah battery stores 5.12 kWh. kWh is the unit to use when comparing batteries of different voltages.
Are these calculators free?
Yes. All three dawnice battery calculators are completely free, require no sign-up, and work on any device. They are designed for installers, B2B procurement teams and facility managers sizing 48V / 51.2V LiFePO4 systems.
Can I use these calculators for lithium and lead-acid batteries?
The formulas work for any battery chemistry, but the default 80% depth of discharge is specific to LiFePO4. Lead-acid batteries should use 50% DoD. dawnice manufactures LiFePO4 batteries — if you are comparing chemistries, adjust the DoD field in the Battery Capacity Calculator.

Need Help Sizing Your System?

dawnice designs and manufactures 48V / 51.2V LiFePO4 batteries, commercial & industrial BESS and containerized energy storage for projects across Europe, Africa, Central Asia and Asia. Send us your load list and we’ll return a free, no-obligation sizing and quotation within 24 hours.

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Free system sizing and quotation for commercial & industrial projects · response within 24 hours.