In short
- LiFePO4 lithium batteries last 3,000 to 6,000 cycles and weigh two to four times less than lead ones for each Wh they store.
- Lead-acid batteries (flooded, gel and AGM) last 800 to 3,000 cycles. AGM can be deeply discharged; many gel batteries can’t.
- None of them is simply “safe”: all need proper use, ventilation and no short circuits.
- A car battery isn’t suitable for an inverter or solar panels.
First things first: a home battery has to be deep-cycle
With an inverter, a power station or solar panels, the battery is drained quite a lot and recharged over and over. That’s deep-cycle use, and not every battery can take it. A car battery, for example, is built to deliver a kick of current to start the engine and recharge right away. According to PVEducation, the solar energy course from Arizona State University and UNSW, it wears out quickly if drained often and shouldn’t be used in a solar system. Our beginner’s guide explains this in more detail.
The two families: lithium and lead-acid
Almost every home battery belongs to one of these two families. Here are their figures according to Australia’s national science agency (CSIRO):
| Type | Cycle life | Years of life | Energy per kilo | Recommended temperature |
|---|---|---|---|---|
| LiFePO4 lithium (LFP) | 3,000–6,000 | 3–15 | 90–130 Wh/kg | −20 to 60 °C |
| NMC lithium | 3,000–6,000 | 3–15 | 100–205 Wh/kg | −20 to 60 °C |
| Lead-acid | 800–3,000 | 3–12 | 30–50 Wh/kg | −20 to 50 °C |
| Advanced lead-acid | 3,000–6,000 | 3–12 | 30–50 Wh/kg | −20 to 50 °C |
What it means in practice: to store the same energy, a lead battery weighs two to four times as much as a LiFePO4 one and, in general, handles fewer charge-discharge cycles. The ranges are wide because they depend a lot on the maker and on how the battery is used.
LiFePO4 lithium (LFP)
It’s a type of lithium battery that uses iron and phosphate. According to CSIRO, its advantages are that its materials are cheap and abundant and that it handles charging and discharging very well. Its weak point is that each cell delivers a little less voltage than cobalt-based lithium, so it stores somewhat less energy per kilo than NMC.
On safety, precision matters. LiFePO4 is often called “the safest”. A 2024 study by the universities of Sheffield, Imperial College and St Andrews, which reviewed published research on the gases lithium batteries release when they fail, found that’s an oversimplification: NMC batteries release more gas, but the gases from a failing LiFePO4 battery are more flammable and more toxic. The useful takeaway is that no chemistry lets you skip using it properly.
NMC lithium (nickel, manganese and cobalt)
It’s lighter for each Wh it stores, which is why it’s used where weight matters. According to CSIRO, its drawback is that it contains cobalt, which is expensive and scarce.
Flooded (liquid) lead-acid
The classic type, with liquid inside. According to PVEducation, it handles deep discharges and lasts a long time, but needs maintenance: you have to check the liquid level and top it up with distilled water, and occasionally give it a stronger charge so the liquid doesn’t separate into layers. It gives off gas while charging, so it needs a ventilated spot.
Gel lead-acid
The liquid is thickened into a gel. Its advantages, according to PVEducation: less gassing, almost no maintenance and little chance of spilling acid. Its drawbacks: it needs a carefully controlled charger to avoid damage and, above all, many gel batteries use plates that don’t handle deep discharges well. If you’re buying one for an inverter, check the maker sells it specifically as deep-cycle.
AGM lead-acid
The liquid is soaked into a glass-fibre mat. According to PVEducation, it can be deeply discharged without losing life, and it handles fast charging and discharging and a wider temperature range. Its drawbacks are that it costs more than a flooded one and also needs a controlled charger.
How far to drain each one
The more you drain a battery each time, the shorter its life. CSIRO gives this example for lithium batteries: drained fully every time, they lasted 180 cycles before losing 20% of their capacity; drained to 80%, 300; to 50%, 1,300. That’s why our battery calculator suggests using 80% of a lithium battery. For deep-cycle lead batteries, PVEducation mentions discharges beyond 50% and up to 80%; the calculator uses 50%, the cautious choice, and you can change it.
Safety and recycling
- Keep batteries somewhere ventilated, especially flooded lead ones, and away from anything that can burn.
- Keep tools and metal objects away from the terminals: a short circuit can destroy the battery.
- A punctured or leaking lithium battery can catch fire or release toxic fumes: stop using it and contact the maker.
- A dead battery doesn’t go in the trash: lead batteries contain toxic lead and acid, and lithium ones can catch fire. Take it to a recycling point.
So which one should you choose?
- If you’ll use it often (frequent power cuts or solar panels every day): a LiFePO4. It handles far more charge-discharge cycles, weighs less and needs no maintenance. CSIRO notes that lithium batteries are now often the cheapest, smallest and lightest option for a home.
- If it’s for the occasional power cut and the purchase price matters most: a deep-cycle lead battery can do the job. If you want no maintenance, AGM; if you choose gel, check it’s deep-cycle.
- Never a car battery.
To work out what size you need, use our power outage battery calculator.
Sources and references
- CSIRO (Australian Government), 2021. Batteries for Homes: rechargeable batteries for domestic energy storage.
- C. Honsberg and S. Bowden, PVEducation. Lead Acid Batteries.
- pv magazine, April 10, 2024. How safe are lithium iron phosphate batteries?, on the study by the universities of Sheffield, Imperial College and St Andrews, “Review of gas emissions from lithium-ion battery thermal runaway failure – Considering toxic and flammable compounds”, Journal of Energy Storage.
Frequently asked questions
Is LiFePO4 the same as lithium?
It’s one type of lithium battery, the one that uses iron and phosphate (also called LFP). According to CSIRO, it lasts 3,000 to 6,000 cycles and its materials are cheap and abundant. Other lithium types, such as NMC, weigh less but contain cobalt.
Which is better for an inverter, gel or AGM?
According to PVEducation, AGM can be deeply discharged without losing life, while many gel batteries don’t handle deep discharges well. If you choose gel, check the maker sells it as deep-cycle. Both need a controlled charger.
Can I use my car battery with an inverter?
It’s not a good idea. It’s built to deliver a kick of current to start an engine and wears out quickly if drained often. An inverter needs a deep-cycle or lithium battery.
