Lithium in the Classic Hymer in 2025 - no real reason not to - and busting the myths about Lithium.

First draft - Sep 2025

You can now buy a 100ah smart Lifepo4 with Bluetooth for £200 or a bit less. This means that the price is now only about £50 above a good quality lead acid battery. 

For the extra £50 you get a battery that will last at least 10 times longer and will give you at least 50% more usable power. But most importantly, you will get a battery that will talk to you! This is the "smart" part of the name - unlike a traditional lead acid battery, smart lithium batteries have a brain which monitors the battery and it will talk to you via an app on your phone or tablet.

This is the most important and powerful feature for motorhome owners - information. But be warned that not all 12v lithium batteries are smart with Bluetooth, so make sure you see Bluetooth in the specification. 

Once you have a smart lithium battery in your van and an app in your hand, you then get to know everything that is going on in your battery system. The brain in the battery, known as a BMS - battery management system - tells you exactly what the voltage is, and how many amps are flowing in and out and how many you have left. For a motorhome owner, this information is invaluable because it puts you in control with no more nasty surprises. In the old days you never knew how much power you had left until the lights went dim. Now all you have to do is look at the app.

So why doesn't everybody rush out and buy one? 

The answer is complicated. It is a combination of fear of new technology, a belief that it is expensive, and whole raft of internet memes and stories preaching doom gloom and confusion.

Fear of new technology is reasonable - it has always been so. There is always an adoption curve with a new technology, and there are always geeks and early adopters who can't wait and get in first - they pave the way for the rest of us. In the case of lithium batteries for motorhomes, I now firmly believe that they are now in the mainstream, and that lead acid batteries are now "old technology".

It is the same for the money side. Lithium used to be 10 times the price, and now it is not. The reasons for this are simple - electric cars and China. The batteries are now being churned out in such huge quantities that the prices have plummeted. The lithium battery market is now even bigger than the old lead acid battery market, because the lithium batteries in electric vehicles are far bigger than the old fashioned starter batteries. 

But the doom gloom and confusion question is a lot harder to answer - harder, but certainly not impossible. I have been monitoring the situation for many years and my conclusion is quite simple - bad news travels fast on the internet, good news does not. What has happened is that a few stories from the early days have become internet memes, and the biggest of these is that "lithium batteries can't just be swapped for lead acid batteries", and worse, that they "will cause damage".

But these stories are not just made up out of thin air - there have been negative stories from the early days of lithium, but as with many other stories online, they have grown in the telling, been embellished, adopted by armchair experts, and then quoted as fact. The trade have also played their part, and adopted their arguments either to preserve their existing business by doing down new technology, or promoting it as "must only be installed by professionals". The rest has been a huge amount of confusion and hearsay - no wonder the average owner gets confused.

Unfortunately to explain all this away I now have to get into technical details, but I will try and keep it simple.

Let's take the damage side first - where did these stories come from? They came from the press coverage of several major incidents in recent history. The most famous of these were the battery fires in the new Boeing 787 in the first year of its life, the crash of a DHL cargo plane that was blamed on a consignment of lithium batteries and the famous case of the Samsung phones catching fire in your pocket. And we can all add to these the many stories we see online of electric cars on fire. There are plenty of other stories too and the collective belief has become - lithium is dangerous. And the actual truth is - yes it is! But only if badly handled. But you also have to remember that there are several types of lithium battery and they all have different characteristics. In response to the early problems, there was a scientific race to improve the safety of lithium batteries, and the result was Lifepo4. This stands for lithium iron phosphate and is the safest type of lithium battery ever made, and is the only type used in leisure vehicle applications. And it is very safe - safer than lead acid in most respects. But the old stories still linger that "lithium" is unsafe.

The other aspect of the "damage" memes, is two sided. Either that you will damage your old lead acid setup if you just drop a Lifepo4 battery into it, or that the battery itself will be damaged if you do.

Let's address the last one first. It is just wrong. A Lifepo4 battery has a BMS and the purpose of the BMS is to protect the battery. It does this by monitoring everything, non stop, in real time. If it detects anything outside of the ordinary, it simply shuts the battery down and isolates it. Overcharge it, it shuts down, over discharge it, it shuts down, too hot or cold? It shuts down. In fact it is just about impossible to damage a Lifpo4 battery with electricity or temperature - it just shuts down, and stays that way until the problem goes away. And helpfully, because it is smart, it will tell you via the app why it has done this, which is a great aid to troubleshooting. 

So why the myth? I believe it is because of the first aspect, that damage to an old setup can be caused, and that damage has just been expanded to mean any damage. So let's move on to the question of damaging an old lead acid setup by just changing the battery from lead acid to lifepo4, and nothing else. 

The maximum charging voltages of both battery types is 14.4 to 14.7v. In reality, charging systems in a classic motorhome are generally around 13.8v to 14.4v - so there is no danger there, and don't forget, if you did drop a Lifepo4 into a system that had a (faulty) charging voltage in excess of this - guess what! It would shut down - unlike a lead acid battery that would get hot and start to fizz and smell - and there are plenty of internet stories about that.

So there is no danger the a Lifepo4 battery it is protected. So what about the other components in a motorhome setup - the charge sources. There are 3 charge sources in a modern motorhome. The alternator, the 230v EHU charger, and solar, if fitted.

But before we progress to discussing each of these in turn, let's address the one area where a Lifepo4 battery is different to a lead acid battery - it has a lower internal resistance. This means in simple terms that it is capable of taking more charge and will take that charge until it is full - which means that it will charge quicker. In many respects this is a good thing for a motorhome owner. You want your battery to recharge in as short a drive as possible, or to take full advantage of sunny weather, or a quick plug in to EHU.

But while this is generally a good thing, it also has a down side, and this down side particularly manifests itself in old classic motorhomes, because in many instances, the equipment is old - the alternator, the EHU charger, the solar system - they could very easily be 30 or even 40 years old. So what happens is that sometimes, but it is by no means definite, when you swap a lead acid battery for a Lifpo4, some of the components might suddenly be asked to work a bit harder, and occasionally this extra work might be the final straw that pushes an already tired component over the edge and into failure. And what happens then? The latest change gets the blame - the new battery. And because bad news travels fast on the internet, before you know it - it's "lithium battery killed my charger", or alternator, or whatever.

But there is no technical reason behind this - all that happened was that the charger was ready to give up anyway. Or the alternator, or the split charge relay, or the main fuse that you didn't even know was there. But it wasn't the battery.

Everything is old in a classic motorhome. Long before lithium came along, these situations were common. Take chargers as an example - pre 95 Hymers left the factory with 10a chargers and 100ah lead acid leisure batteries. As the vans got to 25 years old these were famous for breaking, and many were replaced. In fact it is quite rare now to even find an original still installed. But they are perfectly capable of charging a Lifepo4. I have taken original chargers and put them on my workshop bench connected to Lifepo4 batteries and tested them for days and weeks. 

Same for alternator charging. The original classic Hymer split charge relay system is designed for 20 amps - that's why the Strom meter on the panel only goes up to this figure. And it is all that the cabling and relay system is capable of carrying. Hymer designed it this way. Most classic Hymer alternators were only about 60 amps or so, so you don't want too much additional load. With headlights on and the wipers going full tilt, pulling away from a festival on Monday morning with an empty leisure battery - that's when the 30 year old alternator finally gives in and shouts "enough!"

So the point I am trying to make is that these stories derive from old age and circumstance, and can be rarely if ever be blamed on the battery, whether it be Lifepo4 or lead acid. Nothing lasts for ever. 

So what to do? How can you be sure? The answer comes free with the Lifepo4 battery - it is in the box! When you have an app in your hand that tells you exactly what is going on you can identify potential problems in advance, and be ready for them. Here are some practical examples. Let's say you have the original 10a charger and you install a 100ah Lifepo4 battery. You can run a test - with nothing else connected, plug in the van and see how much power the charger delivers to the battery - the app will tell you exactly. In most cases you will not even see 10a - because the charger and cabling may be old and tired. Same goes for the alternator - you want to see about 20a - the app will tell you. Ditto for solar.

This information will inform you and enable you to make decisions. 

Finally I want to address the other online meme about Lifepo4 - that you have to change your charger, fit a 2b (battery to battery charger), or change your solar controller because the old one does not have a "lithium profile". A lot of this is based on the fact that when somebody goes online and asks the question, somebody has to answer. And the most plausible answer is the one that advises you to "upgrade". So people do! But for a basic installation it is usually not necessary.

However there is one instance where this advice is sound and that is when you want to install biggeer batteries. There is a lot of fun and pleasure to be had from messing with motorhome electrics. And one of the great advantages of lithium is that it is capable of packing a lot of power in a small space. 200ah, 300ah and even more, are now affordable and capable of being installed in classic motorhomes. This gives owners the chance to run high power stuff like hairdryers, coffee machines, toasters, kettles and air fryers ... and many do. But if you do increase the battery capacity of your motorhome beyond the original 100ah, you can, but then of course it follows that your charging systems also need to be upgraded - not for any technical reason, but for practical reasons. Every amp you take out has to be replaced, so you want to do this as fast as is practically possible. This is where the stories come from - it is not that you "have" to, it is that you "should" because it makes sense. You can in theory, safely charge big batteries with the old setups - but it would just be too slow!

But everything in an old classic is delicate, so when you are trying to get more power into a battery, these things have to be carefully considered. Some of the decisions are easy, such as installing a bigger charger. Same for solar - install bigger panels, and if you are upgrading panels, then you will be buying new modern controllers, and these will have lithium profiles - no brainers. And in the case of old alternators where you don't want to overload them, the advice is generally don't try to pull more than about 50% of the alternator power to charge a big leisure battery. And the easiest way to do this is to install a b2b of the required capacity - there are other ways, but a b2b is the easiest, and if you have just spent £600 on a big battery, you can afford a b2b at £120 ....

But if all you are doing is replacing an old 100ah battery with a new 100ah Lifepo4, you can, just make sure it is smart, with Bluetooth, and that after you install it, use the app to keep an eye on it. And in pure classic Hymer terms - the pre 95 models - there is no reason why the original charger and relays can't cope with a Lifpo4. If you do have problems, it won't be the battery's fault - they were bound to happen sooner or later anyway. You can't damage a Lifpo4, and Lifepo4 is a very safe battery technology. Any problems you do have are easily fixed. 

There does happen to be a "sweet spot" for a higher power classic Hymer lithium installation. In terms of the space available for the batteries, the space on the roof, the way the cabling is set up ... I call it a "quad 3" setup. Most roofs will take 300w of panels - the front part of the roof will take a 1500 x 1000 300w panel perfectly, unless there is already a small rooflight there, over the front bed. Victron make a lovely high quality 30a charger - also bluetooth, and I have fitted more of these than any other. And with most alternators being around 60 to 80a - then a 30a b2b charger is just right. And a 200a or 300a Lifepo4 battery can be made to fit in most vans. So all these numbers have a 3 - 300ah of Lifepo4, 300w of solar, 30a charger and 30a b2b. This makes for a well rounded and versatile system. It will support a 12v compressor fridge, which is becoming a popular upgrade. It will support an inverter that will power those desirable coffee machines and airfryers. It will make the most of the roof space, to maximise solar energy, and give you the most you can reasonably expect from your engine and each hour of driving, and a 30a charger will give you a full battery from empty on just an overnight charger, minimising the time that EHU is needed. Such a "quad 3" setup at 2025 prices should cost no more than £1000 (not including inverter) - and that is using all Victron. This can often be reduced considerably if existing or cheaper gear is used. 

And a final note for post 95 van owners who are saying "what about vans with a EBL?" .... the short answer is - pretty much the same - there is no reason for you not to have exactly what you want - a 100ah smart lithium will work with an EBL, and for bigger battery setups, the EBL can be bypassed and just used for 12v distribution. I have done many of these, but there are 3 or 4 different EBL models and each has different requirements, so to write an article that covers everything would be long and confusing. I have diags and ideas for most EBLs so best to contact me or ask on the group.