Voltage Drop and Our Insatiable Need for energy
The subject of battery systems can be a bit dry. So get yourself some Classic Coke (my favourite) water (nature’s favourite) or white rum & coke (Heiner’s favourite) and let’s dive in.
Sidestepping the risk of being a bit too dry, I’ll present this using a few analogies.
Its 16 years ago and my Land Cruiser has a 100a/h AGM house battery in the engine bay. The charge system consists of two thick cables directly from the start battery. Once my day’s drive is done, the AGM has received a good charge and my cokes are cold. To prevent discharge of the start battery overnight, I rotate the big cut-off switch between them. In the morning my cokes are still cold, but by the following afternoon camped under an acacia, I can see the voltage has dropped and I’m concerned that my cokes, milk, cold meats and cheese will not stay cold through the night. As I use the energy stored in the AGM, the voltage steadily drops, until at around 45% of battery charge, it’s reached the voltage where the fridge shuts down. At around 11V.
In crude terms, a 12V AGM lead-acid with the load of just one small fridge, is well charged at 13V, around half charged at 12V and flat at 11V. And it will reach 11V with about 45% of its energy inaccessible, because it can only be released at lower than useful voltages. With my AGM direct connection, due to voltage drop, the charge at best could only reach about 90% of battery capacity. Had I used one of those awful solenoid switches instead, at best I’d get around 80% charge. If the cables had been long, then 75%. And so on. That means a 100a/h AGM battery at 75% charge, only a meagre 30a/h is actually usable. Every connection causes voltage drop. Every line of cable adds to it. The sum voltage drop is a function of the number of connections, the quality of the crimps and the connections, the lengths of cable and the thickness of those cables. And it adds up, fast. A drop of more than 0.4V in a 12V system is barely tolerable to keep the system working. For years we coped with these systems, until one year things got a lot better.
It's 15 years ago and I’ve swapped the big switch for a new technology called DC-DC charging. The unit was made by Ctek and promised a constant 10A to the battery. That is less initial charge current than the cables I swapped it for, but being a constant 10A triggered by the ignition, it will maintain voltage all the way through the charge cycle. It charged the house battery to near 100% of its capacity. So, which charging system is better? The answers lie in how much time will I be driving between stops, and how long is each stop? These questions are still relevant today even with the biggest and best systems.
DC-DC charging has this magic trick because the voltage drops caused by the things mentioned are almost entirely cancelled out – but only if its wired properly as close to the house battery as possible. DC-DC chargers adapt the charge current based on the voltage it reads at the house battery itself. No direct connection system can do this and it makes all the difference.
It’s 10 years ago and my Land Cruiser has 2x75a/h Lead Crystal batteries (A short-lived technology that was a forerunner to lithium) set up with a Redarc DC-DC charger rated at 40A. While driving, a charge of 40A reached the house battery until at about 95% charge when the rate slowed and floats close to 100%. The 150a/h capacity and a battery type that could accept far higher charge rates than AGM, Lead Crystal gave me more usable energy, charged faster. I never got to find out exactly how much better because the lithium battery revolution happened at the same time. Namely, the extraordinary mating of LiFePO4 and DC-DC charging technologies. LiFePO4 means that 95+% of the battery capacity is now usable and with DC-DC chargers engineered for LiFePO4, they can accept charge rates far exceeding anything yet seen.
And as LiFePO4 developed, better and smarter internal battery management systems keep them safe and extend their lives – which are 10 times longer than lead-acid in all its forms.
So in a matter of a few years, the world of 12V systems in 4x4s, trailers and caravans became unrecognisable. But it must be said, that some flat-Earthers still think AGM is the best ever.
Its two years ago and as part of testing the EGON DC-Hub Dual that is suitable for multiple chargers, my Land Cruiser had both 40A and 25A DC-DC chargers feeding 2x200a/h Amptron LiFePO4 batteries. I might have had huge storage capacity and lightening charge rates compared to 20 years ago, but I still had to drive all day to charge the batteries! Added to my fridge and lights, I had an electric water heater, a 12V marine oven, induction cooking and a Starlink running for most of the day. This system, if built into my Land Cruiser 20 years ago, could easily have sustained my needs without driving for two weeks. With my current demands, I need to drive every two or three days even if I supplement it with solar. To sustain my gas-less energy demands with solar alone, I’d need an array far too large to be practical. Or, I must also use gas and not shower every day and limit Starlink. Which means my needs are outgrowing the technology. That’s not really any different to 16 years ago!
We will always stretch what we have and use what we are given. I could enlarge this system and a 40% increase in charge speeds is possible. But, I’ll need to upgrade the alternator, swap all DC chargers and run even heavier cables. But the charge rates to my trailer, if I pulled one, will be unaffected because of unavoidable voltage drops along long cables and connections to trailers.
But enlarging my system to full-spec seems pointless because even this cannot support a trip I have planned. Up on the northern coast of Western Australia is an extraordinary region called Ningaloo. In high season (winter) it’s too busy and in summer, empty but murderously hot. But the evenings, mornings and nights are nothing short of magical. And that means I need to park off in my van with the air-con running most of the day. Even with the biggest 12V system, shore power is the only way to do that. That is not the idea here! But there is now a feasible solution. You’ve guessed it. 48V. It changes everything. Not only is it possible, it’s not even very complex or expensive.
Almost all significant issues with voltage drop, charge current limitations and inefficiencies are erased with 48V. Voltage drop is 4 times less impactful on efficiency and the higher voltage means that losses everywhere are reduced, also by a factor of four.
Heiner and I will be releasing reports as we continue to test the extraordinarily simple EGON 48V architecture and prove our claims that it can fill that same battery not in a day, but in an hour. Bigger and bigger batteries do not solve the fundamental problem of off-grid power if you cannot charge them efficiently. In fact, the speed and efficiency of recharging is arguably more important than capacity, especially when current demands are high. And this will be the case when I add an aircon to my rig.
A 48V system has now also been installed by the first workshop, (Unwind Designs, VIC) so a second vehicle has joined the test fleet. January 2026, and 48V systems will be installed in two more; a V8 Landcruiser and a 3.0 Hilux. We are making this SpaceX performance available to workshops across Australia and South Africa, with roll outs starting April 2026.
Thank you for being with us at this exciting time.
Andrew and Heiner
Listen to Andrew's podcast here.