Battery terminology guide

Solar battery terminology explained in plain language

When you start looking at solar batteries, you quickly run into a lot of terms that do not mean much until someone explains them. kWh, DoD, LFP, cycle life, round-trip efficiency — it can feel like you need an engineering degree just to compare two products.

You do not. This guide explains the terms you will actually come across when comparing home battery systems in plain language, the way we would explain them sitting at your kitchen table.

The basics

Capacity and storage — what it all means

kWh — kilowatt hour

This is the main number to focus on when comparing batteries. It tells you how much energy the battery can store. Think of it like litres in a fuel tank. A 10kWh battery stores 10 kilowatt hours of electricity. The average Townsville home uses somewhere between 20 and 40 kWh of power per day, so a 10kWh battery covers a meaningful portion of your evening usage.

Usable capacity vs total capacity

A battery might have a total capacity of 10kWh but only a usable capacity of 9kWh. The difference is a small reserve the battery keeps to protect its cells from being fully drained. When you see a battery spec, check whether the capacity figure listed is total or usable. Most quality home batteries today have a usable capacity very close to their total capacity.

Depth of discharge (DoD)

This tells you how much of the battery’s capacity can be discharged before it needs to recharge. A DoD of 100% means you can use the full capacity. Most modern lithium iron phosphate batteries have a DoD of 90% to 100%, which is why they work so well for home storage. Older battery types had much lower DoD ratings, meaning you were only ever accessing a fraction of the storage you paid for.

Power rating (kW)

Capacity tells you how much energy the battery holds. Power rating tells you how fast it can release that energy. A 5kW continuous power rating means the battery can supply 5 kilowatts of power at any given moment. If your home needs more than that during a peak load, the battery may not keep up on its own. This matters most if you want to run large appliances like air conditioning during a blackout.

Battery types

Battery chemistry — why LFP is the one that matters for home solar

If you see the term LFP on a battery spec sheet, that stands for Lithium Iron Phosphate. It is the chemistry used in every modern home solar battery worth considering, including the Sigenergy SigenStor, GoodWe ESA and BYD systems we install. Here is why it matters and how it compares to older chemistries you might come across.

LFP — Lithium Iron Phosphate

The gold standard for home solar storage right now. LFP batteries are safe, stable and do not overheat the way older lithium chemistries could. They handle deep discharge well, tolerate Townsville’s heat better than alternatives and typically last 4,000 to 6,000 cycles or more. This is what all three battery brands we install use.

NMC — Nickel Manganese Cobalt

An older lithium chemistry used in some early home batteries. Higher energy density than LFP, but more prone to thermal issues and generally shorter cycle life. Most manufacturers have moved away from NMC for home storage. If you are looking at a battery and the spec sheet says NMC, ask more questions about longevity and heat tolerance.

Lead acid

The old technology. You might still see lead acid batteries on some off-grid systems or as cheaper alternatives. They are heavy, can only be discharged to around 50% of their capacity without reducing lifespan, and do not tolerate heat well. In Townsville’s climate they are a poor choice for home solar storage. We do not install them.

How batteries perform

Performance terms worth understanding

Cycle life

One cycle is one full charge and discharge. Cycle life tells you how many times a battery can do this before its capacity drops to around 80% of the original. A battery rated for 4,000 cycles that charges and discharges once per day will last around 10 to 11 years before performance starts to noticeably drop. This is one of the most important numbers when comparing value over time.

Round-trip efficiency

When you put energy into a battery and then take it out again, some is lost as heat. Round-trip efficiency measures how much of the energy you put in you actually get back out. A battery with 95% round-trip efficiency returns 9.5kWh for every 10kWh you store in it. Good modern LFP batteries typically achieve 90% to 97% round-trip efficiency. Higher is better.

C-rate

This describes how fast a battery can charge or discharge relative to its capacity. A 1C rating means it can fully charge or discharge in one hour. A 0.5C rating means it takes two hours. For Townsville homes where peak solar generation and peak evening demand can both be high, a 1C battery is more useful than a 0.5C one because it can take on a full charge quickly and release it quickly when needed. The GoodWe ESA, for example, is rated at 1C.

Self-discharge

A battery that is sitting idle will slowly lose its charge over time. This is called self-discharge. Modern LFP home batteries have very low self-discharge rates, typically around 1% to 3% per month. In practical terms this means a fully charged battery that sits unused for a week will still have most of its charge available. Not something you need to worry about with current home storage systems.

Installation terminology

System and installation terms you will come across

Hybrid inverter

A hybrid inverter manages both your solar panels and your battery storage in one unit. It decides in real time whether incoming solar should go to powering your home, charging the battery or both. If you are installing a battery alongside solar, you need a hybrid inverter. The Sigenergy SigenStor and GoodWe ESA both include one built in.

AC coupling vs DC coupling

These terms come up when retrofitting a battery to an existing solar system. DC coupling means the battery connects directly to the solar panels before the inverter, which is slightly more efficient. AC coupling means the battery connects to the household circuit after the inverter, which makes it easier to retrofit to most existing systems without replacing your inverter. BYD with a Fronius Gen24 is a DC coupled system.

Blackout or backup protection

Not all batteries automatically keep your home running when the grid goes down. This feature is called backup protection or blackout protection, and it needs to be specifically designed into the system. The Sigenergy SigenStor and GoodWe ESA both include whole-home backup. Some battery systems only protect a limited number of circuits. Always confirm this before you buy, especially in Townsville where storms can knock out the grid.

V2H and V2G

Vehicle-to-Home (V2H) and Vehicle-to-Grid (V2G) refer to the ability of a compatible electric vehicle to discharge its battery back into your home or back to the grid. If you have a large EV battery and a system that supports V2H, your car can act as a backup power source for the house during an outage. The Sigenergy SigenStor is the only system in our current range that supports this.

State of charge (SoC)

This is just the current charge level of your battery, expressed as a percentage. 100% means fully charged, 0% means empty. Your battery monitoring app will show you the SoC in real time. You can also set minimum SoC levels, for example keeping 20% in reserve for backup power during a storm event.

BMS — Battery Management System

This is the onboard control system built into the battery that monitors cell temperature, voltage and current to keep everything operating safely. A good BMS prevents overcharging, over-discharging and overheating. You will not interact with it directly but it is doing important work in the background every time your battery charges or discharges.

Quick reference

A quick reference guide to the terms you will see on spec sheets

Term	Short for	What it means in plain language
kWh	Kilowatt hour	How much energy the battery stores. Bigger number means more storage.
DoD	Depth of discharge	How much of the battery you can actually use. 100% DoD means you can use all of it.
LFP	Lithium Iron Phosphate	The battery chemistry used in modern home solar storage. Safe, long-lasting and heat tolerant.
SoC	State of charge	Current charge level of the battery as a percentage. Like a fuel gauge.
BMS	Battery Management System	The onboard system that keeps the battery operating safely by monitoring temperature, voltage and current.
C-rate	Charge rate	How fast the battery charges or discharges. 1C means it can fully charge or discharge in one hour.
V2H	Vehicle to Home	Your electric vehicle can send power back to your home during a blackout.
V2G	Vehicle to Grid	Your electric vehicle can send power back to the electricity grid.
Cycle life		How many full charge and discharge cycles the battery can handle before capacity drops noticeably.
Round-trip efficiency		How much of the energy you put into the battery you actually get back out. Higher percentage is better.

Common questions

Battery questions, answered

How long will a solar battery actually last?

A modern LFP battery rated for 4,000 cycles, charged and discharged once per day, will last around 10 to 11 years before capacity drops to 80% of its original rating. In practice, many batteries last longer because not every day is a full cycle. Most quality home batteries come with a 10-year warranty.

What is a good round-trip efficiency for a home battery?

Anything above 90% is considered good for a home battery. The systems we install all achieve 90% or better. The difference between a 90% and a 95% efficient battery is small in day-to-day terms but adds up over years of daily use.

Does battery chemistry matter for Townsville's climate?

Yes, and it is one of the reasons we only install LFP batteries. Townsville’s heat is harder on battery chemistry than cooler climates. LFP handles elevated operating temperatures better than older lithium chemistries and does not carry the same risk of thermal runaway. Where you install the battery in your home also matters. We will advise on the best location to minimise heat exposure during the site visit.

What does modular mean when it comes to batteries?

A modular battery is one where you can start with a base capacity and add extra battery modules later to increase storage. All three battery systems we install are modular. This means you do not have to buy your maximum capacity upfront. You can start with enough for your current needs and expand if you get an EV, upgrade your air conditioning, or simply want more backup capacity down the track.

Is a higher kWh battery always better?

Not necessarily. A battery that is much larger than your evening power draw will rarely fully cycle, which means you are paying for storage you are not using. Getting the size right for your actual usage is more important than getting the biggest available. We review your Ergon bill and usage patterns before recommending a size.

Ready to find the right battery for your home?

We assess your usage, your existing setup and your goals before recommending anything. No pressure, no guesswork.

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