When it comes to choosing a battery for your 12V setup – whether it’s for a caravan, 4WD, boat, or off-grid system – one of the biggest questions people ask is: Should I go with AGM or lithium?
At first glance, the decision often comes down to one factor: price. On the surface, AGM batteries are usually cheaper than lithium. It’s easy to look at the price tag and assume AGM is the better deal. But that assumption doesn’t always hold up when you take a closer look.
In this article, we’ll explore the real cost of AGM vs lithium batteries – not just at the checkout, but across the full life of your setup.
Upfront Cost vs Lifetime Value
There’s no denying it: AGM batteries cost less upfront. If you’re on a tight budget or just dipping your toes into off-grid adventures, AGM might feel like the safer option. But to understand the true cost, we need to look beyond the initial purchase and factor in:
- Usable capacity
- Cycle life
- Performance efficiency
- Replacement frequency
Once these elements are factored in, lithium starts to pull ahead.
Depth of Discharge: Why It Matters
One of the most important – and often overlooked – differences between AGM and lithium is depth of discharge (DoD). This refers to how much of the battery’s capacity you can safely use before needing to recharge.
- AGM batteries are typically recommended to be discharged to 50% of their rated capacity to preserve lifespan.
- Lithium batteries, on the other hand, can comfortably discharge to 80–90% without damaging the cells.
That means a 100Ah AGM battery gives you around 50Ah of usable power, while a 100Ah lithium battery gives you up to 90Ah. That’s nearly double the usable capacity from the same size battery.
So while lithium costs more per amp hour upfront, the cost per usable amp hour is significantly lower.
Cycle Life: How Many Times Can You Use It?
Another key advantage of lithium is its lifespan. Lithium batteries are designed to last thousands of charge cycles – often 2000 to 5000 cycles depending on usage. AGM batteries typically last around 300 to 500 cycles under similar conditions.
Let’s do some rough maths:
Here's the same information in a graph, to help you visualise just how much of a difference this is:
Even though lithium costs more at the start, over time it delivers more than 10 times the usable energy before needing replacement.
Weight and Efficiency Bonuses
While this post is focused on cost, it’s worth mentioning that lithium batteries also offer practical savings through:
- Lighter weight – reducing fuel use in caravans or 4WDs
- Faster charging times – reducing generator or alternator runtime
- Low self-discharge – retaining charge longer in storage
- High efficiency – minimal energy loss between charge and discharge
These factors can save time, fuel, and frustration – all of which have value in the real world.
Total Cost of Ownership
Let’s reframe the question. Instead of asking “Which battery is cheaper?”, ask “How much power will I get for every dollar I spend?”
While AGM batteries appear more affordable at first, you’re paying for:
- Less usable capacity
- Shorter lifespan
- More frequent replacements
Lithium batteries cost more up front, but:
- Deliver far more usable power
- Last significantly longer
- Offer better performance in demanding environments
When you calculate the cost per cycle or per usable amp hour, lithium batteries come out on top almost every time.
So, Which Should You Choose?
It depends on your needs and budget:
- If you're building a budget-conscious setup or only use your battery occasionally, AGM may suit you for now.
- But if you want long-term savings, higher performance, and fewer battery replacements, lithium is clearly the more economical choice over time.
If you’re already investing in solar panels, inverters, and other off-grid gear, lithium is often the smarter companion that helps you get the most out of the rest of your setup.
