About Camper batteries

If you want to stay offgrid, somehow you have to have power from somewhere that you can consume. Whether you want a light to read by, an outlet for your laptop or to charge your phone, that power has to come from somewhere. And in this article I want to see where the energy comes from, how it is stored and how it is consumed from different types of batteries. Let's review them in the first phase and see what we really end up with:

We have the normal lead acid car batteries, then we have deep cycle gel, we put lithium-ion in the list although meh and lithium iron polymer or lifepo4. The lead-acid battery is designed for traction, i.e. to give you power to start the car. It is not designed for constant consumption and will deteriorate quickly. We also get rid of Lithium-ion because they are not really common and they are quite dangerous, sometimes having quite interesting and violent exothermic reactions. We're sticking with deep cycle and lifepo4, which we'll call lithium from now on for ease.

We will compare the batteries according to several criteria: purchase price, weight, lifetime, number of cycles and DoD or depth of discharge, total production. Sure, we can go into much more detail but we said let's just focus on the most important stuff. I would make a mention here that we are talking about standard lithium batteries and not aftermarket balancing cell variants or DIY solutions. Sure, they can be done, but it's a hassle and 3 out of 5 people I know who have had them done have problems with them. So, to keep the balance, we take 2 batteries from the same manufacturer and compare them.

We will choose a Victron AGM 100Ah and a Victron LiFePO4 100Ah also, that is 1280Wh or 1,28kWh. Of course, the first thing we notice is the very, very different acquisition cost. On Darcom Energy's website, the AGM version is 1800 RON and the lithium version 7100 RON and from there things separate quickly. The next easily intuited difference has to do with weight, and I find that to be an extremely important aspect of a camper. In the case of the 100Ah variant, the lithium is less than half the weight of the AGM. As capacities increase, the difference becomes 1 in 3 or even 1 in 4, as deep cycle batteries are usually quite heavy. We will come back to the question of weight in relation to Depth of Discharge, because it is a very important issue. So we've established so far that lithium is lighter and more expensive. We call these elementary empirical observations.

Moving on, we come to life as number of cycles, which is influenced by this Depth of Discharge. A deep cycle battery has an optimum DoD of 50%. This means that out of 100Ah in our standard battery, we can use 50Ah before it starts to degrade quite seriously. In the data sheet on Victron's website, they inform us that at 50% discharge we have 600 battery cycles. Good. So in the life of this battery, we can use 600 times each 50Ah. To keep a balance, we still stay at 50% DoD and look at the lithium data sheet. For the same specifications, in the 2022 version of the batteries, with a similar DoD, the same battery supports 5000 charge cycles, so 8.3 times more cycles. But this is not the most relevant feature of these batteries, or lithium in general, but the fact that they support a DoD of 80%, where they have 2500 cycles. So unlike a deep cycle where you can draw 50Ah from a 100Ah battery, here you can draw 80Ah from a battery of the same capacity. The normal lifespan of a gel battery is 5-7 years, whereas the lifespan of a lithium battery is 15-20 years, so add that to the list of notable differences.

And here we come back to weight, because we originally calculated the weight at purchase, which defines how much you pay FAN Courier to get your battery home. But now, with the new data, we calculate according to available energy. If we can get 80Ah out of the lithium battery and it weighs 15 kg, to get the same energy out of the gel we need a 160Ah battery weighing 47 kg. And lo and behold, I added a black ball to the gel, or white to the lithium, or whatever you want to call it.

With all this information, we go back to costs and there are two important aspects: the price per kWh at purchase and the price per kWh over the lifetime of the battery. Clearly, gel wins hands down at 1400 RON per kWh while lithium jumps to 5500 RON per kWh. Let's go back a bit to the number of cycles and DoD to calculate the lifetime price per kWh. We take strict DoD 50%, and for gel we will have 50Ah i.e. 0,6kWh x 600 cycles so 360kWh over the lifetime. For lithium we have 50Ah, so the same 0.6kWh x 5000 cycles so 3000kWh over the lifetime of our battery. We divide by the purchase price and the result is that gel costs 5 lei per kWh and lithium 2.36 lei per kWh, so less than half.

To recap: cost of acquisition, 1-0 to gel. weight 1-1, recover lithium, DoD 2-1 for lithium. 3-1 life cycles for lithium. Price per kWh purchase, point for gel, so 3-2. Finally, price per kWh per operating period, 4-2 for lithium. And then there was the difference in lifespan from ... let's say 7 years on gel, as I'm feeling generous, and 15-20 years on lithium. So 5-2 and the match is over. I agree that this option has a higher purchase price, but together we have shown that you actually come out better on every relevant score. For a long time I've been trying to get these calculations down on paper. I'm sure I misspoke here and there, I said watts instead of watts hour or whatever. I'm sure we'll find out together where we went wrong from the comments. But I really wanted to cover this topic in more detail because, more than anything else, the batteries in the gloria the sprinter sparked the classic reaction: They're expensive, ladies. So, overall, I can say with certainty that no, they are not at all expensive compared to some gel batteries. And I haven't gotten into the details of how it loads and unloads yet, there's another fantastic drama I want to discuss in a future episode, notably geekier than this one. But these batteries are the definition of "I'm too poor to buy cheap stuff."

Now that we've talked about how you size a system and what batteries you put in, in the next blog we'll talk about solar panels and the controllers that ... well ... control them. And there we have to split the difference and it is as important as the batteries. I hope you enjoyed the text and I hope to read you soon!