In the first post of this series, I explained the chief downsides of lead acid batteries, the type found powering the house bank in 99.999% of all RV’s you have ever seen.
It is a depressingly long list.
As you will soon see, on paper lithium ion batteries seem to be superior in almost every possible way – as if Zeus himself had climbed down from Olympus and handed the world the perfect battery. Or maybe it wasn’t Zeus, but that annoying pink Energizer Bunny, bringing the gift of divine electrons pulsing to the rhythm of his eternal drum.
To understand the promise and potential of lithium ion batteries for RV use, it helps to first understand the myriad of ways that lithium ion batteries differ from lead acid.
The Lithium Difference
Lead acid batteries are made from (not surprisingly) a mixture of lead plates and sulfuric acid. This was the first type of rechargeable battery, invented way back in 1859.
Lithium ion batteries on the other hand are a much newer invention, and have only been around in a commercially viable form since the 1980’s.
Lithium technology has become well proven and understood for powering small electronics like laptops or cordless tools, and has become increasingly common in these applications – edging out the older NiCad (Nickel-Cadmium) rechargeable battery chemistry due to lithium’s many advantages.
But as you might recall from the many news stories a few years ago around defective laptop batteries bursting into flame – lithium ion batteries also earned a reputation for catching fire in a very dramatic fashion. The commonly used lithium ion battery formulation had been Lithium-Cobalt-Oxide (LiCoO2), and this battery chemistry is prone to thermal runaway if the battery is ever accidentally overcharged. This could lead to the battery setting itself on fire – and a lithium fire burns hot and fast.
Just imagine how nasty the fire would be if it was a large battery burning, and not just a small laptop battery!
This is one of the reasons that up until recently, lithium was rarely used to create large battery banks.
But in 1996 a new formula for mixing lithium ion batteries was developed – Lithium Iron Phosphate. Known as LiFePO4 or LFP, these batteries have a slightly lower energy density but are intrinsically non-combustable, and thus vastly safer than Lithium-Cobalt-Oxide.
Now that large scale LFP batteries are starting to be massed produced (primarily targeting the electric vehicle market), we are now on the cusp of LFP batteries becoming practical for RV use!
And once you consider the advantages, LFP batteries becomes exceedingly tempting.
The Amazing Advantages of Lithium Ion Batteries
To understand just how substantial these advantages are, be sure to read the parallel list about the downsides of lead acid batteries…
Superior “Useable” Capacity
Unlike with lead acid batteries, it is considered practical to regularly use 80% or more of the rated capacity of a lithium battery bank, and occasionally more. Consider a 100 amp hour battery – if it was lead acid you would be wise to use just 30 to 50 amp hours of juice, but with lithium you could tap into 80 amp hours or more.
Extended Cycle Life
Laboratory results indicate that you could expect to see 2,000 to 5,000 cycles out of a well cared for LiFePO4 battery bank, which means that a lithium ion battery bank has the potential to likely outlast your RV! These are theoretical results – we are looking forward to seeing how lithiums do in reality for RV use, as the energy uses of a home-on-wheels is not normal laboratory conditions, nor at all similar to that of an electric vehicle (which is where LFP is primarily used right now).
In contrast, even the best deep cycle lead acid batteries are typically only good for 500-1000 cycles.
Fast & Efficient Charging
LiFePO4 batteries can be “fast” charged to 100% of capacity. Unlike with lead acid, there is no need for an absorption phase to get the final 20% stored. This can save you hours of generator run time. And, if your charger is powerful enough, lithium batteries can also be charged insanely fast. If you can provide enough charging amps – you can actually fully charge a lithium ion battery just 20 minutes!
But even if you don’t manage to fully top off to 100%, no worries – unlike with lead acid, a failure to regularly fully charge LFP batteries does not damage the batteries.
This give you lots of flexibility to tap into energy sources whenever you can get them without worrying about needing to do a full charge regularly. Several partly cloudy days with your solar system? No problem that you can’t top off before the sun goes down, as long as you’re keeping on top of your needs. Only 30 minutes left until quiet time at the primitive campground? No worries – with lithium, you can charge up what you can and not fret about leaving your battery bank perpetually undercharged!
Very Little Wasted Energy
Lead acid batteries are less efficient at storing power than lithium ion batteries. Lithium batteries charge at nearly 100% efficiency, compared to the 85% efficiency of most lead acid batteries.
This can be especially important when charging via solar, when you are trying to squeeze as much efficiency out of every amp as possible before the sun goes down or gets covered up by clouds. Theoretically, with lithium nearly every drop of sun you’re able to collect goes into your batteries. With limited roof & storage space on RVs for panels, this become very important in optimizing every square inch of wattage you’re able to mount.
Especially combined with the fast charging ability, this also translates to less fuel costs when running your generator to charge the batteries.
Fewer Placement Issues
LiFePO4 batteries do not need to be stored upright, or in a vented battery compartment. They can also fairly easily be assembled into odd shapes – an advantage if you are trying to squeeze as much power as possible into a small compartment. This is especially useful if you have an existing battery bay that is limited in size, but you want or need more capacity than lead acid is currently able to provide.
Little Maintenance Requirements
Theoretically, lithium batteries should be fairly maintenance free. An occasional “balancing” process to make sure all the cells in a battery bank are equally charged may be called for, but a well designed energy management system should (ideally) do this automatically.
But to be fair, while we are in the experimental phase with our own lithium battery system, they are far from maintenance free as we endeavor to tweak the system. Until we perfect our setup, we are watching our batteries vigilantly.Remember, this is newer technology and barely even tested for RV use. Inverters and chargers do not yet come standard with profiles for LFP. The battery distributors and manufacturers are still tweaking the energy management systems that protects the batteries too. This is new and evolving tech, and not quite yet ready to be “plug and go”.
AGMs have an advantage here, just set your charger to “AGM Mode” and you are good to go.
Peukert’s Losses & Voltage Sag Virtually Non Existant
The discharge curve of lithium batteries (especially relative to lead acid) is essentially flat – meaning that a 20% charged battery will be providing nearly the same output voltage as an 80% charged battery. This prevents any issues caused by the “voltage sag” common to lead acid as they discharge, but does mean that any battery monitor or generator auto-start dependent upon voltage levels will likely not work well at all when monitoring a lithium bank.
On the flip side, once lithium batteries are fully discharged, their voltage takes a nose-dive quickly – which is why tweaking your energy management systems to protect the batteries to absolutely never let this happen is vitally important. Completely discharging a lithium ion bank, even once, can render your entire pack permanently dead.
Another huge advantage of lithium batteries is that Peukert’s losses are essentially non-existant. This means that LiFePO4 batteries can deliver their full rated capacity, even at high currents. Whereas lead acid can see as much as a 40% loss of capacity at high loads. In practice, this means that LFP battery banks are very well suited to powering high current loads like an air conditioner, a microwave or an induction cooktop.
Size & Weight Advantages
And finally, the reason why most folks are intrigued by lithium… LFP batteries are much smaller & lighter!!!
The 12-volt 100 Amp Hour LiFePO4 battery packs we started with when building our system are 4.9″ x 11.0″ x 9.2″, and weigh just 28.2 lbs. That works out to be 0.282 lbs per amp hour of capacity.
A Trojan 8D-AGM 230 amp hour battery on the other hand weighs 167lbs, which works out to be .726 lbs per amp hour – which is about 2.5 times heavier.
And when you take “usable” capacity into account, the weight advantage of lithium is even more dramatic. Remember, that 100 amp hours of lithium will deliver 80 amp hours, no matter the discharge rate, without worry. 230 amp hours of AGM can only deliver 70- 115 amp hours, depending on the discharge rate.
So not only is lithium smaller and lighter than AGM per amp hour, you need significantly less stored amps to get the same usable capacity.
To simplify what we’ve covered so far about Lithium Ion vs. Lead Acid AGMs, here’s this handy chart we created:
As you’ve seen, the theoretical advantages of LiFePO4 batteries for RV use are exceedingly compelling, particularly if you boondock a lot, use solar and/or want to minimize generator use. But we all should remember about the difference between theory and practice…
In theory, there is no difference.
In practice – using LiFePO4 for RV house batteries remains new and uncharted waters.
And that brings us to the biggest downsides of lithium batteries – the cost and the novelty.
These uncharted waters don’t have a low cost of entry, particularly when compared to the Walmart specials on generic flooded lead acid batteries. And there are not a lot of resources you can turn to for tech support since the technology is so new. Most inverter / charger makers don’t even officially support lithium batteries yet at all. So those opting to try lithium for RV use are pioneers, and need to educate themselves to fully understand what they are dealing with.
If you consider the lifetime cost, and the fact that lithium batteries should (theoretically) far outlast even the best high-end AGM’s, suddenly the math starts to look compelling.
I’ll dive into explaining how we weighed the lifetime costs vs the benefits, and will give the details on the costs and specifics of our new system in my next lithium post. Stay tuned!
By the way, we should note – we are not trying to motivate anyone to follow us on this path. We are not selling these batteries, we are not affiliates with any battery dealer, we paid for all our components and nor do we have any financial stake in the technology beyond our own systems. We are simply full time RVing technomads who are designing our own cutting edge home & office on wheels, and are sharing our research & project. Of course we’d love to have more folks out there pioneering and helping us take the arrows in our backs. Right now, we do not consider this technology ready for the mainstream, and those contemplating this technology need to be a bit savvy with electrical and battery technology.
Other Posts In this Series: