The heart and soul of any good 12V system is the battery (or batteries) you choose. They can legit make or break how good your set-up is.
You’ve probably heard a lot about lithium batteries over the past few years. How great they are, how they’re the future of off-road power supply, how much better they are than traditional AGM batteries.
As Han Solo said, it’s all true. Except that lithium isn’t the future. It’s the now (Han Solo didn’t say that part, I just made that up).
What’s the story?
In today’s world, there is literally only one reason (sorta) to keep on with AGM batteries. And that’s the initial purchase price. In every other way lithium is better, hands down, and the price disparity is strongly offset by the fact that lithium costs about double an AGM yet lasts four times longer (on average). So while the upfront cost is higher, the value for money is twice as good.
However, not all lithium batteries are created equal. Some have a deceptively low number after the dollar sign. While others seem over-priced to the point of absurdity. Then there are outputs – which mean slightly different things to AGM outputs. And they come in all different sizes and shapes. While we’re asking, why can’t you use your current AGM battery charger on lithium anyway?
Obviously, the task of choosing the right battery for your needs is quite the rabbit hole, and what works for your mate may not be the best option for you.
That’s why we thought we’d throw together this handy guide to choosing the right lithium for your rig. Everything you ever wanted to know about selecting the right unit for your needs but were too afraid to ask.
Three things you need for a lithium system
1. A lithium battery (duh) with enough amps to support your required current draw. Keep in mind that lithiums can be drained a lot more than a lead acid battery. So 100Ah lithium is roughly equal to 200Ah AGM.
2. A charging set-up. These can range in (cost and features) from smart isolators to DC-DC chargers to Battery Monitoring Systems.
3. Optional extras. It’s not a bad idea to have solar incorporated and to have a means of charging your battery from a 240V outlet onboard. A pure sine wave inverter for 240V accessories will never go astray either.
When comparing lithium to AGM batteries there are probably six key areas where lithium is bigger, faster, stronger and better looking than the old-school AGMs.
They’re lighter. In today’s world of stretching a vehicle’s GVM to the limit with accessories and towing capacities, being able to save weight wherever you can becomes more and more important. As a general rule, comparing same size lithium and AGM batteries, the lithium will weigh roughly 33% what the lead acid guy will. That’s a massive saving. Considering a decent sized AGM can weigh up to 40kg or so. For the same weight, you can run double or triple the amount of batteries with lithium.
They have more useable capacity. You need to understand two terms here. Amp hours (Ah) and depth of discharge (DoD).
A deep cycle battery’s capacity is measured in amp hours. The more Ah a battery has, the longer it can last before needing to be recharged basically. DoD is the percentage of rated capacity (say 100Ah for example) that a battery can be drained to before it’s essentially useless.
A 100Ah AGM has a DoD of 50%, so once it’s drained halfway it is no longer able to keep your accessories powered up.
A 100Ah lithium has a DoD of 90%, so it’d need to be drained almost completely before it reaches its failure point. You can use the battery for longer without recharging without risking damage to the battery.
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They last longer. Battery life is measured by the number of cycles (aka each time it’s charged and discharged) it is expected to last at a particular depth of discharge. A good quality lead acid AGM will last for around 1000 cycles at 50% DoD. Cheaper batteries may only last for half that.
Lithium batteries are usually rated around 5000 cycles. And can be capable of even more if looked after appropriately.
A lead acid battery may last you 3 years if you’re lucky. A lithium can last up to ten years – so that initially higher purchase cost has paid for itself about halfway through the battery’s lifespan.
They charge faster. If you’ve ever had to recharge a lead acid car battery you’ll know it’s a multi-stage process. Usually it goes bulk, absorb and float over several hours, if not overnight.
Lithiums have much lower internal resistance. So they don’t need any stages of charging. More importantly, they can accept a higher charge rate, so they’re recharged much faster.
This lower resistance also means that energy can be recovered from solar panels at a greater rate – which is ideal for us four-wheel drivers.
They provide more power. Remember high school electrical theory? Power (in Watts) is found by multiplying Volts by Amps. So, if a battery holds its voltage over a cycle (which lithium does, and AGMs do not) and is able to discharge more amps (lithium yes, AGM nah) then it’s going to pump out more power.
High end lithium batteries are capable of peak outputs of around 500A (or more). And can continuously put out around the 200A mark. Lithium also maintain their output rates over the period they’re being discharged. Whereas lead acids drop off significantly the lower their state of charge gets. Or in other words, lithium simply takes a bat to lead acid batteries.
Wait, lithium can be cheaper?
They cost less over the life of the battery. We’ve already covered this but it bears repeating. Let’s say a lead acid battery costs $300 and a lithium costs $1000. The lead-acid will likely need replacing in three years’ time. Whereas the lithium will last 10 years. $300 at 3-year intervals means that at year 9 you’re about to drop your 1200th dollar on your fourth battery while the lithium is still going strong. And that’s not even counting the fact that lead acid AGMs are often more expensive and lithiums often last longer than 10yrs if managed well.
Working out the right capacity
This one is highly subjective and comes down to the 12V gear you’re wanting to run while at camp. Working out the total current draw and adding a little on top for security. We’ve put together a case study of a common set-up below.
Let’s say that you want to run the following while the vehicle is off at camp, factoring in an hourly usage amount for each accessory:
A 60L chest fridge (24hrs a day)
LED camp lights X2 (4 hours at night)
Phone charger (2 hours to get your phone from 10% back to 100%)
The fridge will roughly require 45Ah per day from your battery, your pair of camp lights around 16Ah (2x (2A x 4hrs)) per day, and your phone charger will use 3Ah (1.5A x 2hrs). Some quick mental gymnastics later and our total is 64Ah per day.
In this case a 100Ah lithium will be more than enough for a comfortable overnight stay, or with a little charge from either solar or a quick drive of your 4X4 each day to get some electrons topped up from the alternator, you could comfortably run this set-up almost indefinitely.
We need to have a talk about how effective lithiums are at taking a charge and why it’s important to you. We’ve already ascertained that lithium charges quicker than lead acid. A 30A charger will bump a lithium up from flat to fully charged in about three hours. The same 30A would take at least 10 hours to do the same for an AGM battery.
But where it’s even more useful is when you’re parked up at a beautiful spot for a few days and are running off solar. Let’s say you’ve got a 170W panel directly facing at the sun and, for argument’s sake, it’s working at full efficiency pumping all 170W into your auxiliary battery. Watts divided by Volts (12V) is around the 14A mark topping up your battery. With lithium’s low resistance, each and every one of those amps is feeding straight into topping up any lost charge. With AGM, it’s barely maintaining the battery at its current level.
Oh, and many batteries these days come with built-in chargers too, which is handy.
You win again, lithium.
Size kinda does matter (so does shape)
The last couple of years has seen the lithium game explode (not literally) with innovation. You’ve got Victron offering batteries that can pump out a frankly astonishing 330Ah (with a 400Ah peak rating). You’ve got lithium batteries that are a straight replacement for your starter battery that’ll provide a cool 1400+CCA (that’s winch-truck numbers folks). There are 200Ah slimline batteries on the market.
What it all comes down to is how many Ah (for deep cycle applications) or CCA (for high current draw aka winches and starters) you need and go from there. Of course, you’re also going to have to decide…
Where to fit them
Lithium batteries come in all different capacities and even shapes, so choosing the shape that’s going to suit your vehicle becomes an important decision.
If space is at a premium (think most dual-cab utes) then fitting a slimline lithium behind the rear seat on a specially made bracket will be an excellent use of otherwise wasted space. Most behind the seat spaces will allow fitment of a 110Ah battery, which is plenty for running the fridge and lights at camp.
In wagons, lithiums can also be fitted in front of drawers, behind cargo barriers or even stashed behind interior trim panels (LC200s are perfect for this).
Under-bonnet used to be a no-go for lithiums due to the heat build-up, however these days there are a few companies (iTechworld, DCS and Invicta spring to mind) that are selling lithium batteries that have been specially developed to handle the engine bays temps. These have opened up possibilities for those folks who wanted lithium power but had nowhere to put it or had already invested in a second under-bonnet battery tray. The excuses well has finally run dry, pal. Sorry not sorry.
Do you need a battery app?
You speak to your Mum on an app. You order your late-night shame kebab delivery on an app. You watch re-runs of Friends and Buffy the Vampire Slayer on an app (no judgement, Sarah Michelle Gelly is an icon!), so why wouldn’t you keep an eye on your 12V settings via your phone or tablet as well?
Yep, pretty much every brand of lithium battery has a Bluetooth option that beams info like state of charge, time until flat, depth of discharge and dozens of other handy little tidbits straight to you phone without you even having to get off your camp chair.
It’s like living in a live action The Jetsons movie, isn’t it?