Whether you're running a fridge in the caravan, keeping the lights on at a bush campsite or powering a small off-grid shed, it all comes down to one thing: the battery. A deep cycle battery is built to deliver steady power for hours and then be recharged again and again, which is exactly what you need when you're away from mains power.
The big question most people face is whether to go with a trusty AGM battery or spend more on lithium. This guide explains what deep cycle batteries are, the main types you'll find in Australia, what they cost in 2026 and how to pick the right size for your setup.
What is a deep cycle battery?
A car's starting battery is designed to give a huge burst of power for a few seconds to crank the engine, then get topped up straight away by the alternator. It doesn't like being drained.
A deep cycle battery works the other way. It delivers a smaller, steady current over a long time, like running a 12V fridge overnight, and it's designed to be drained and recharged over and over. That's why deep cycle batteries are used in:
- Caravans, campervans and motorhomes
- 4WD dual battery setups
- Boats and marine use
- Small off-grid solar systems for sheds, cabins and farms
- Portable power packs for camping
Using a regular car battery for these jobs usually ends badly. Repeated deep draining can kill a starting battery quickly.
Types of deep cycle batteries
Flooded (wet cell) lead-acid
The old-school option. Cheap, but needs regular topping up with distilled water, must be kept upright and releases gas while charging, so it needs ventilation. Less common in caravans these days.
AGM (absorbed glass mat)
An AGM battery is a sealed lead-acid battery where the acid is soaked into glass fibre mats. It's maintenance-free, spill-proof and can be mounted in different positions. For years it has been the go-to deep cycle battery for Australian campers.
Gel
Another sealed lead-acid type that uses a gel electrolyte. Handles heat and deep discharges fairly well, but charges slowly and needs the right charger settings.
Lithium (LiFePO4)
Lithium iron phosphate batteries are now the popular upgrade. They're much lighter, last far longer and let you use more of their capacity. They cost more upfront, though the gap has been shrinking.
AGM battery vs lithium: the honest comparison
Here's how a typical 12V 100Ah AGM battery compares with a 12V 100Ah lithium (LiFePO4) battery in 2026:
| 12V 100Ah AGM | 12V 100Ah lithium (LiFePO4) | |
|---|---|---|
| Typical price | About $280 to $400 | About $900 to $1,200 |
| Usable capacity | About 50Ah (keep above 50% charge) | About 80 to 90Ah |
| Weight | About 28 to 30kg | About 12 to 14kg |
| Cycle life | About 400 to 600 deep cycles | About 3,000 to 5,000 cycles |
| Real-world lifespan | About 3 to 5 years of regular use | About 10 to 15 years |
| Charge time | About 6 to 8 hours | About 2 to 4 hours |
| Cold weather | Loses some capacity, but charges fine | Most won't charge below 0°C |
Two things stand out. First, a 100Ah AGM really only gives you around 50Ah of usable power if you want it to last, while a 100Ah lithium gives you most of its rating. So to match one lithium battery, you'd often need two AGMs, which doubles the weight.
Second, while lithium costs about three times as much upfront, it can last three or four times longer. Over 10 years, the cost per year often ends up roughly similar, and you get the weight savings and faster charging along the way.
Deep cycle battery prices in Australia (2026)
Prices vary by brand, capacity and where you buy, but here's a rough guide:
| Battery | Typical price range |
|---|---|
| 12V 100Ah AGM deep cycle | About $280 to $400 |
| 12V 120 to 135Ah AGM | About $350 to $550 |
| 12V 100Ah lithium (LiFePO4) | About $900 to $1,200 for established brands |
| 12V 200Ah lithium | Often around $1,500 to $2,500 |
You'll see cheaper lithium batteries online, some for a few hundred dollars. Be careful. Quality varies a lot, and the battery management system (BMS) that protects the cells matters. Stick with brands that offer a solid Australian warranty and local support.
How to choose the right deep cycle battery size
Battery size is measured in amp-hours (Ah). To work out what you need:
- List your 12V devices and how many amps each draws. A typical 12V fridge might average around 2 to 4 amps, LED lights under 1 amp each, and a phone charger about 1 to 2 amps.
- Multiply amps by hours of use per day. For example, a fridge averaging 3 amps over 24 hours uses about 72Ah a day.
- Add everything up to get your daily use in Ah.
- Allow for usable capacity. For AGM, double your daily use. For lithium, add about 20%.
- Add a buffer for cloudy days or extra nights without charging.
Example: if you use about 80Ah a day, you'd want roughly 160Ah or more of AGM capacity, or around 100 to 120Ah of lithium, for one day without charging. For longer trips, plan on solar panels or a DC-DC charger to top up while you drive.
Charging a deep cycle battery properly
Good charging is the secret to a long battery life:
- Use the right charge profile. AGM, gel and lithium all need different settings. Using the wrong one can shorten battery life.
- DC-DC chargers are the best way to charge from a modern vehicle's alternator. Many recent models have a lithium setting.
- Solar panels with a regulator can keep your battery topped up at camp.
- Don't leave AGMs flat. Lead-acid batteries that sit discharged can be permanently damaged. Recharge them as soon as you can.
- Store batteries charged and in a cool, dry place when not in use.
If you also have rooftop solar at home and are thinking about a home battery, that's a different kind of system. Our solar battery price guide covers whole-home batteries.
Which deep cycle battery should you buy?
An AGM battery suits you if:
- You camp a few times a year rather than touring full time
- You want the lowest upfront cost
- Weight isn't a big concern
- Your existing charger only has lead-acid settings
Lithium suits you if:
- You travel often or for long periods
- You're watching weight in a caravan, camper or 4WD
- You want more usable power from a smaller battery
- You want a battery that lasts a decade or more
Safety tips
Deep cycle batteries store a lot of energy, so install them carefully. Use correctly sized cables, fuses or circuit breakers, secure the battery so it can't move while driving, and keep terminals covered. Lithium batteries should have a quality built-in BMS. For permanent installations in vehicles, caravans or boats, have the wiring done or checked by a qualified auto electrician or marine electrician.
Frequently asked questions
What is the difference between an AGM battery and a deep cycle battery?
Deep cycle describes what a battery is designed to do: deliver steady power and be drained and recharged many times. AGM describes how it's built. Many AGM batteries are deep cycle batteries, but some AGMs are designed for starting engines instead.
How long does a deep cycle battery last?
A good AGM deep cycle battery typically lasts around 3 to 5 years with regular use. A quality lithium (LiFePO4) battery can last around 10 to 15 years.
Can I charge a lithium battery with an AGM charger?
It's not recommended. Lithium batteries need a charger with a lithium profile. Many modern chargers and DC-DC chargers include one, so check your charger's settings first.
How many hours will a 100Ah deep cycle battery last?
It depends on what you're running. A 100Ah AGM gives about 50Ah of usable power, which could run a fridge drawing 3 amps for roughly 16 hours. A 100Ah lithium gives about 80 to 90Ah, closer to 27 to 30 hours for the same fridge.
The bottom line
A deep cycle battery is the heart of any caravan, camping or small off-grid setup. AGM batteries are affordable and dependable for occasional use, while lithium costs more upfront but is lighter, gives you more usable power and lasts much longer.
Work out your daily power use, size your battery with a sensible buffer, use the correct charger and buy from a brand with a solid Australian warranty. Get those right, and your battery will keep the fridge cold and the lights on for many trips to come.
Prices and specifications are general estimates as of October 2026 and vary by brand, model and retailer. Always check manufacturer specifications and have permanent installations done by a qualified electrician. See our disclaimer for more.
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