But let me be honest from the beginning - very few people will actually need 600ah. I was actually planning 300ah, which was a meaningful upgrade from my original 200ah lead acid setup. But at the last minute a friend who was advising me said that for what it will cost - all other installation costs being the same, an extra £600 to double the capacity was, on paper, a bargain. Furthermore he said that he had found, with that much power on tap, that there were many more intangible benefits that would crawl out of the lithium woodwork. And he was right!
Background - my wife and I full time in our S700 in all seasons. We are also heavy power users. TV and laptop are on most days, most of the time. Our daily power use varies but averages about 75ah a day. Our original fully charged 220ah lead acid battery, backed up with 500w of solar, would, in winter, just manage a full weekend off grid, with no engine charging or EHU. In summer we had power to spare, and could stay off grid almost indefinitely. But for full timers, it is winter performance that matters.
In winter, our routine was always different to our summer routine. In winter we needed to drive more, and plug in more, which meant using camp sites or visiting friends more often, or even occasionally running a generator. We never liked using it, but occasionally - maybe twice a year, it was a life saver.
Of course there is also the point to be made that you can always use less power - this is a valid point, and we can and do switch things off if we want to stay put for longer and eke out the battery, but it's no fun.
This last system, we ran for about 5 years, and it taught us a lot about energy use in a motorhome. We discovered 3 things. 1. accurate monitoring is essential - you need to know what you have and what you have left - same a the van fuel gauge. 2. No matter what, every amp you take out, has to be put back in. 3. Solar power is by far the most important part of any off-grid system.
1. Monitoring I have blogged about elesewhere. It's important. But I would add that in the context of lithium batteries, you usually get it for free - in an app, and this has proved to be a real benefit.
2. This sounds self evident, but is really important! In summer, a decent solar system will put in the next day all you took out the night before. But in winter, solar panels give a fraction of what they do in summer, so you have to monitor very carefully and plan your activities to put back in power from other sources.
3. Solar power is the only free source of power, and the only one you can be truly off-grid. So in a nutshell, you need to fit as much as your roof will hold.
The reason I make these 3 points is that having a huge battery is not the simple answer to all these problems. But what it does do, is give you options.
One example of this is that with 600ah on tap - whereas before we would have to move after 3 days - now we can stay for much longer. If we use 200ah over a weekend, we still have 400ah left. However we soon learned that if we do stay in one place and use say 90% of a 600ah capacity, then we really need a proper recharge. Winter sun would take weeks to recharge that much, so the reality has proved that if we do need 500ah of recharge, the only meaningful option is to plug in. So our EHU charger has to be capable of completely refilling a 600ah batter in an overnight charger - this basically means 10 to 12 hours at 50a. So another rule we have learned about big lithium, is that your EHU charge source needs to be big enough to recharge in less that 12 hours - ie overnight.
The same goes for alternator charging. A lithium battery will suck in every amp that you throw at it, so a 60a alternator will deliver exactly that, for long periods of time, and will eventually overheat. There are various ways to improve this - we chose to install a B2B - battery to battery charger. This is a unit that sits between the engine battery and the lithium battery, and limits the power that can be transferred. In our case this is 60a - half the capacity of our 120a upgraded alternator. A side effect of this is that with a 60a b2b, 2 hours of driving actually gives us 120a. This is quite different to our old lead acid battery, which would suck in high power for a short while, and then settle down to a fraction of that - so a 2 hour drive would give something like 30a of charge, even though 60a was theoretically available. This is quite technical, and down to the difference in charging characteristics of lead acid and lithium, but this is a noticeable example.
This also a good example of how fitting a lithium battery means that you also have to think about, and if necessary modify, your charging equipment. Lithium batts have different charging characteristics to lead acid batteries. In our case this proved to be a good thing, because as already mentioned in the past, especially in winter, we had to plan our movements carefully, especially with regard to the weather, and driving distance - now we have a decent B2B, we can drive less for the same power, or get more power from the same drive. So when we are just touring around, distance between stops can be less, saving diesel. It also means that with a 50a EHU charger, we can take advantage of even short stops where EHU is available - ie at friends etc.
But by far and away the biggest advantage for us has been simply the fact of having all that power on tap. We no longer have to move because we have to - we move because we want to. We can stay a week or more instead of just a weekend, and if we do, and use almost all of that 600ah - then we know that all we need is an overnight charge, and we are good to go again. In pure financial terms, with campsites and CLs costing around £15 these days, in winter we are saving around £60 a month.
There have also been some minor advantages, but satisfying nevertheless. We now run our fridge on 220v while driving - this keeps it cooler. And in summer we run it on 220v quite often, even though it is a 3-way fridge and takes 10amps. This is saving us gas - LPG, and we have already noticed that we are using less gas. I have always defended 3-way fridges because they are the ultimate in versatility, and they are. Our 3-way is quite new, so no intentions of throwing it out for a compressor fridge, but if the situation arose, I would now have no problem handling a compressor fridge, even in winter.
Another advantage is the use of high power items. My old system was easily capable of delivering the 100a or so needed to run a toaster or coffee machine for a few minutes, and on paper, because they were only on for a few minutes - eg 100a for 5 mins = 8.3ah - not a lot. But over the months I soon noticed that regular high power use was changing the characteristics of my lead acid battery. I looked into the technicalities of this, and learned that the capacity (and long life) of a lead acid battery depends entirely on the type of discharge it is asked to perform. It will last longer with only light discharge, and shorter with heavy discharge. And because I have accurate monitoring, and am a bit of a geek, it didn't take me long to realise that these morning coffee and toaster sessions were affecting the battery noticeably. 10 minutes of breakfast use was taking much longer to recharge from solar than the numbers would suggest. So after a year or so, we stopped, and went back to gas for toast and coffee. No such problem with lithium - they are quite linear. Doesn't matter if you take out 100a in 1 hour or 1a in 100 hours - the result is the same. So although the basic rule of put back in what you take out still applies, there is no worry about affecting the life of the battery.
Don't forget what I said above - these are minor advantages, but I have enjoyed discovering them and experimenting.
So do you need 600ah?? Probably not is the honest answer. But several of us full timers have, and nobody yet is regretting the extra cost. 300ah is probably a meaningful upgrade for most van livers upgrading from 100 or 200ah lead acid systems. My system is now 6 months old and I have yet to go below 300ah, but I know it's there, and I expect to be using it for the rest of my van life - 10 to 20 years - which is another good reason to go lithium - long life.
There are 2 ways to get lithium. DIY or ready made. I chose the DIY route. The DIY route involves buying the individual 3.2v Lifepo4 lithium battery cells, and connecting them together, in a case or frame of your own construction, to the power and voltage you want. So in my case I used 8 x 3.2v 300ah cells, in a 4 series 2 parallel configuration, giving 600ah at 13v. The mechanics and connections was a relatively easy DIY job. A lithium battery consisting of multiple cells needs a circuit board called a BMS - Battery Management System. This is a board that sits between the cells and the outside world. It has multiple functions - it balances the cells, and protects them from over and under discharge and voltage. It is an essential part of the system. Good BMS also have bluetooth built in and come with an app. That is all the technical detail I will go into at this point. But anybody with a multimeter, who knows how to use it, has hooked up batteries and stuff before, and is willing to read online from the many excellent DIY websites and forums - is capable.
The non DIY route is to buy from an established battery manufacturer. These companies do what I have just described above, but in a much more user friendly way - ie they put the 4 cells and the BMS inside a box that looks and feels like a traditional 12v battery. These can usually, but not always, be straight swap replacements for old 12v lead acid batteries - but you should check with the supplier. You also get UK based support backup and warranty. A typical example in the UK is Roamer batteries, who consistently get good reviews. But the cost difference is about 50 to 100% over DIY, because you have to pay their profit margin, which is well deserved!
Lastly - order cells directly from China at your peril. BMSs are usually OK, but ordering small quantities of lithium cells can be a nightmare from China, using Alibaba etc. Just take my word for it, and don't be tempted by what appear to be really cheap prices in dollars - that is only the beginning of it. Contact me more more details.
