Calculate energy and runtime
Size a battery using watt-hours, amp-hours, usable capacity and a measured load.
Explore toolsEstimate usable capacity, battery runtime and charging needs. Learn how lithium battery chemistry, inverter efficiency, solar generation and lifetime costs affect real projects—from an overnight power cut to a full home storage upgrade.
*Illustration assumes 85% DoD and 92% inverter efficiency. Configure the calculator below for your own system.
A battery project is easier when you separate power, energy, charging and economics. Browse these starting points before getting lost in product specifications.
Size a battery using watt-hours, amp-hours, usable capacity and a measured load.
Explore tools →Assess daily energy demand, solar surplus, backup reserve and overnight needs.
Explore tools →Review compatible charging, current limits and temperature protection.
Explore tools →Connect DC battery energy with actual AC loads and inverter efficiency.
Explore tools →Learn what nominal voltage, ageing and different chemistries mean.
Explore tools →Plan critical circuits and calculate realistic backup hours before buying.
Explore tools →Enter your battery and AC load details to see nominal energy, estimated usable output and approximate run time. This tool calculates steady-load examples, not an approved electrical design.
Use the battery manufacturer’s nominal specifications wherever possible.
Please enter valid positive values. Percentages must be between 1 and 100.
A transparent sizing approach is better than choosing a battery by its advertised amp-hours alone. Work from what you need to run, and only then compare specific products.
List the equipment you intend to operate and use a watt meter, nameplate or realistic average duty cycle to estimate the energy actually consumed.
Multiply load in watts by hours of use. A 500 W continuous load for eight hours requires 4,000 Wh of delivered energy.
Apply a sensible usable-discharge fraction plus inverter losses, then make an allowance for future battery ageing and practical reserve needs.
Confirm inverter output, short startup surges, BMS limits, approved wiring, charging compatibility and all manufacturer conditions separately.
Three battery specifications can look similar on a product page while meaning different things. Knowing what each value represents helps prevent costly sizing mistakes.
A 100 Ah battery at 12.8 V holds about 1.28 kWh nominal energy; a 100 Ah battery at 51.2 V holds about 5.12 kWh. Both show the same amp-hour number, but the second represents four times as much nominal energy. This is why kWh is often more useful when comparing household battery systems at different DC voltages.
In most home storage settings, a product’s usable-capacity figure is more meaningful than its advertised nominal-capacity figure. Usable energy may already account for manufacturer-defined reserves, so avoid subtracting depth of discharge twice if the technical sheet already quotes usable kWh.
Loads vary. A refrigerator cycles on and off, some inverters have a baseline idle draw, and discharge performance changes with temperature and age. High surge current at startup is a separate issue from all-night energy demand. Calculate both average energy and the maximum simultaneous power you expect the system to supply.
For an existing practical example, the site's home backup sizing guide explains how to separate backup duration from system power. The published battery sizing tool is another useful starting point when you already know your daily kWh demand.
These are transparent worked estimates. They are not claims about any manufacturer’s performance, and each example assumes a constant average load.
At 85% permitted discharge and 92% inverter efficiency, about 4.00 kWh is delivered to an AC load. A steady 500 W load would run for approximately 8.0 hours. This is a simplified estimate, not a guaranteed duration.
4.00 kWh usableIf a device averages 80 W and the entire power station delivers 85% of the advertised energy at its AC sockets, its estimated runtime is 10.9 hours. Idle draw and peaks may shorten it.
≈ 10.9 hA home using 6 kWh from evening to morning would need around 7.7 kWh nominal battery capacity at 85% DoD and 92% conversion efficiency, before any reserve margin.
≈ 7.7 kWh nominal“Lithium-ion” describes a broad family. Cathode chemistry can affect nominal voltage, energy density, thermal behaviour, service conditions and lifetime expectations. The exact cell and battery pack still matter more than a chemistry label alone.
| Consideration | LiFePO4 (LFP) | NMC-type lithium-ion | LTO-type lithium-ion |
|---|---|---|---|
| Common strength | Longevity and stationary-storage suitability | Energy density for limited space or mass | High power and long-cycle applications |
| Nominal cell voltage | Typically around 3.2 V | Typically around 3.6–3.7 V | Often around 2.3–2.4 V |
| Typical use context | Home solar storage and auxiliary systems | Many EVs and portable devices | Specialised, demanding duty cycles |
| Key purchasing check | Installed BMS and approved charger | Pack thermal management and warranty | System voltage and cost trade-offs |
| Important limitation | Voltage-only SoC estimation can be weak | Thermal, cycle and model-specific trade-offs | Lower energy density often means more weight |
Values are general chemistry examples, not the ratings of your particular pack. See the LiFePO4 vs NMC comparison and the three-chemistry guide for more context.
Solar battery value depends on when your panels generate electricity, when you consume it, local tariff rules and how much stored energy can actually be recovered.
For many solar households, the first useful number is overnight usage. If evening and overnight appliances consume 5 kWh, a battery advertising 5 kWh nominal capacity may not cover it after discharge and inverter losses. Work backward from delivered energy, not nominal capacity alone.
Energy tariffs can change the economics. A system that saves electricity purchases at a high peak price may have different financial results from one that mainly shifts solar exports to a lower-value period. The website's solar and battery bill reduction tool explores this decision, and battery ROI calculator helps frame total installed cost against annual savings.
Rated solar array output does not equal constant charging power. Weather, season, panel orientation, other household loads, inverter efficiency and the battery’s charge limits may all reduce the power available to storage. A quick “battery kWh divided by panel kW” calculation is a lower-bound illustration, not a prediction of tomorrow’s charging time.
The published off-grid cabin guide expands on autonomy and seasonal margins. Installers should confirm inverter compatibility, supported communication protocols, and any local interconnection requirements.
Use these shortcuts for transparent energy and current calculations. They are educational arithmetic tools and do not set safe charge or discharge limits.
Convert nominal battery charge and voltage into stored electrical energy.
Express charging or load current relative to a rated amp-hour capacity.
Approximate charging hours at a constant effective charging wattage.
*Real charging can be longer due to current taper and limitations.
A well-designed battery system protects cells from electrical and temperature conditions outside their specified range. The exact limits depend on the model, chemistry and its BMS.
Many rechargeable lithium batteries experience more stress when they are repeatedly subjected to extreme charge and discharge conditions. The relationship is chemistry- and product-specific, so do not apply a universal cycle-life number to every cell. A practical plan balances available capacity today with the battery manufacturer’s cycle and warranty conditions.
Our existing depth-of-discharge guide introduces those trade-offs. The battery warranty guide also discusses why a cycle count alone does not fully describe the economic life of storage.
Lithium cells do not all tolerate the same charging conditions. Charging certain batteries outside their allowed temperature range can lead to damage and safety risk. A pack’s low-temperature cut-off, heater functions or charger control must follow the documented design; never override a protective BMS because a battery appears slow to charge.
The published LFP charging-temperature guide and BMS introduction explain what protection systems do. Contact the manufacturer or a qualified technician about actual battery faults.
Protect batteries from physical damage, moisture and excessive temperatures. Do not keep charging packs that are swollen, leaking, smoking, unusually hot or otherwise damaged. When a battery reaches end of life, follow approved battery collection processes rather than placing it in ordinary household waste. Specific procedures vary by jurisdiction and battery form factor.
Installed system cost, energy actually recovered, electricity tariffs, incentives, warranty coverage, future capacity and maintenance responsibilities all influence long-term value.
Compare the installed price to the actual usable energy rather than nominal advertised capacity.
Explore tools →Understand how warranted throughput and cycling affect the long-term value of storage.
Explore tools →Evaluate avoided grid purchases alongside export compensation and conversion losses.
Explore tools →For example, two battery systems might both advertise 10 kWh. If one offers 9 kWh usable and the other 8 kWh usable, comparing them on nominal capacity alone may understate a meaningful difference. A complete comparison should also consider warranted lifetime throughput, inverter replacement costs, installation costs, efficiency and whether a manufacturer restricts warranty coverage by years, cycles or energy delivered.
Tariff savings should always be calculated net of charging losses and other costs. An inexpensive off-peak unit of energy cannot always be shifted into peak hours without conversion loss, and export credits may make storing solar electricity less attractive in some conditions. The right solution depends on local prices and real consumption patterns, rather than a universal payback promise.
These links point to published pages identified in the supplied WordPress export. New draft pages are not linked here until they are ready to publish.
Short answers for sizing, charging, chemistry, energy storage and safety. Check pack documentation whenever a number is important for a real installation.
Multiply nominal voltage by amp-hour capacity to obtain watt-hours. Apply the permitted depth of discharge and any applicable conversion efficiency, then divide usable watt-hours by the average load in watts. Runtime is an approximation because battery voltage, inverter standby draw, temperature and load fluctuations all matter.
An amp-hour describes charge capacity, while a kilowatt-hour describes energy. You also need voltage to convert: nominal Wh = nominal V × Ah, and kWh = Wh ÷ 1,000. Comparing amp-hours across different voltages without converting to energy can be misleading.
LiFePO4, or lithium iron phosphate (LFP), is one type of lithium-ion chemistry. It differs from NMC and other lithium-ion chemistries in voltage characteristics, energy density, thermal behaviour and applications.
It provides an initial energy estimate. Complete system sizing also needs startup surge, inverter continuous power, circuit design, local regulations, battery-BMS compatibility and manufacturer documentation. A qualified installer should evaluate fixed household systems.
Not necessarily. The rating is usually nominal DC energy. Usable battery discharge settings, inverter conversion losses, reserve limits, temperature and ageing reduce actual AC delivery. Manufacturers may quote usable capacity separately.
Charging power can change during the process, especially during constant-voltage taper. Chargers also lose energy and battery-management systems may reduce current for protection. Simple charging formulas should be treated as lower-bound or approximate estimates.
Only roughly, and often poorly. LiFePO4 has a relatively flat mid-range voltage profile, and measurements vary with current and rest time. A properly calibrated BMS or measured coulomb count is generally more useful than a voltage-only guess.
Depth of discharge is the percentage of rated battery capacity used. A battery rated at 10 kWh with an 80% allowed DoD offers up to about 8 kWh of nominal DC energy for that discharge window, before other losses.
It changes the amount of electricity you can recover after charging. For example, 10 kWh added to storage at 90% round-trip efficiency results in about 9 kWh delivered later, before other system-specific losses. Savings depend on tariffs and export values.
Do not charge or continue using a swelling, punctured, overheating or otherwise damaged battery. Follow emergency guidance, keep people away from an actively heating or smoking unit, and contact the manufacturer or your local fire and approved recycling services for safe handling.
LithiumBattery.online brings together practical tools, battery fundamentals and side-by-side comparisons to help readers ask better questions before investing in storage.
We separate nominal capacity from usable output and continuous power from stored energy. Our estimates explain their assumptions instead of implying an exact result for every battery. Product specifications, safety instructions and warranty conditions should be checked directly against up-to-date manufacturer documentation.
Our published editorial policy describes the site’s approach to content. You can review about the site or use the contact page to flag a correction. General research references include Battery University, but no source should replace the technical manual for your specific pack.
Start with your actual load, choose an operating time, and understand the assumptions. Use the calculator now, then read a relevant guide before reviewing equipment specifications.
Calculate battery runtime →