DIY RV Solar System FAQ

DIY RV Solar System FAQ

Due to too frequent deep discharge, the Optima batteries died prematurely in 2022. Test-installed LiFePO4 starter batteries lasted only a few days and had no type of approval for use in the vehicle. So it came about that we have been driving without starter batteries since October 22 and started with the onboard batteries. This is where Renogy’s external BMS has a positive impact. Hardly any other battery provides me with a 24V 700A starting current.

FAQ – background thoughts

Why LiFePO4 and not AGM or GEL?

The heart of the self-sufficient power supply – no matter in which mobile home – is the battery. The battery supplies consumers at night and whenever no power is available from another source. There was no question about which type of battery I would choose. Nevertheless, I would like to give a brief overview to clarify the reasons for my decision.

Do we want to use AGM or GEL batteries or LiFePO4?

The following thoughts and my experience of the last 10 years.

GEL batteries have proven to be robust and durable. They are relatively cheap and still suitable for all holidaymakers away for a few weeks a year. Anyone who usually has shore power access will be just as happy with GEL batteries. The discharge current of these batteries should be at most 20% of the capacity (0.2C)! So be careful with 230V inverters on a small battery bank.

AGM RV battery is characterized by better current delivery – the discharge current can be up to 30% of the capacity, i.e. 0.3C. For this, these batteries require a special charging characteristic of 14.7V. I don’t see any other advantages in AGM batteries. In the last 10 years, 99% of all battery complaints concerned AGM batteries. Some of these gave up their service after just 6 months – often even for no apparent reason. Even with the best care, the batteries were often only 2-3 years old.

LiFePO4 batteries are significantly lighter than the lead batteries described first. They can deliver significantly more energy over their lifetime, which reduces the price per kWh to a good 1/3 compared to GEL or AGM batteries, despite the high acquisition costs. The lithium batteries are extremely high-current capable – so a larger inverter can be operated even with small batteries. Since the batteries should only be fully charged once every 4 weeks to balance the cells, they are ideal for mobile homes, which are primarily only charged with solar systems.

I’ve been living in a mobile home since 2009 – so I use Electricity every day and need to charge the batteries fully at a socket regularly. Even the solar system only sometimes manages to do this in bad weather. Lithium RV batteries are best suited for such an operation because they do not want to be fully charged and can withstand many charging cycles.

Why Renogy batteries and not Winston Thundersky?

I built my first lithium battery myself in 2014 from Winston LiFeYPO4 cells. Then followed, the Renogy Energy LiFePO4 system in the previous motorhome. I was very satisfied with that – unfortunately, from today’s perspective, the batteries were still very heavy because of the built-in Winston LiFeYPO4 cells. With a storage size of 10kWh, that weighs, and I was looking for an alternative.

Fortunately, in 2019 Renogy Energy is just in time to introduce a new 200Ah LiFePO4 battery. The batteries are now significantly smaller and 47% lighter than the previous battery with the Winston LiFeYPO4 cells. The absolute hammer! And as if made for use in the new all-wheel drive truck.

Since we, like most others, have installed the batteries in the living room, they will always be warmer than +5°C, which does not justify the addition of yttrium.

Today I’m wondering whether I would install Renogy LiFePO4 batteries again. Other brands also have great systems. I now use two 12V lithium batteries with 200Ah as a stationary extension, which are connected in series to 24V and parallel to the truck when we are on our property in Portugal. I prefer these batteries today because I don’t have to install an external BMS, and thanks to the high quality of the integrated BMS, I don’t have to worry about failure.

Why not everything on 230V in the vehicle?

You can do that, but you have to consider one thing: Inverters consume Electricity to provide 230V – even if no consumers are connected. A Renogy MultiPlus 12/3000-120, for example, takes almost 2A per hour – even when there is no load.

That’s 650Wh a day!! If you want to be self-sufficient with solar power, a solar output of 250Wp is required in southern Spain in winter to cover this standby consumption from the inverter! Many devices also have a power pack, which converts 230V back into 12V or 24V. There are additional losses.

Why not cook with Electricity?

Why should you cook with Electricity? If the batteries are empty, the kitchen stays cold. Normally, our solar power and battery capacity would be sufficient for cooking with Electricity – but there are situations where sooner or later, you will reach the limit even with such a system. On average, cooking requires about 1kWh of energy per day – with much room for improvement. 1kWh per day must first be generated when you stand under the trees in the forest. The high power when cooking strains the inverter, which can (and will) jeopardize operational reliability at ambient temperatures above 40°C.

Example: Shortly after the start of our trip, it was November in the Black Forest, and we were faced with serious energy problems. Continuous fog and rain pushed the daily solar yield below 0.5 kWh/day. Forget cooking with Electricity if you only have 10kWh storage capacity in batteries! I was glad that the refrigerator and the computers could be operated with it. After four days, the batteries were almost empty – luckily, we could continue driving.

We cook with gas from his 5-kilo tank bottle. I can legally fill this bottle at any LPG gas station throughout Europe. If necessary, I can install grey propane gas cylinders in winter, connect state-owned gas cylinders directly, or transfer them into my tank bottle with a high-pressure hose.

Gas is available worldwide, and the hob will never fail. At most, the nozzle will clog.

A 5-kilo gas bottle has an energy content of 84kWh!!! How many kWh have 400Ah in 24V? Laughable 10kWh!

With one gas filling, we cook for over 4 months! Electricity will never be more reliable!

Nevertheless, we have a portable induction hob with us for the outdoor kitchen and as a backup. If the gas bottle is unexpectedly empty, we can still cook.

We also want to do this with our 1350-watt 230V oven. This is also portable and can be used for bread, rolls and pizza! Here I find a device that runs on Electricity better. Because you can carry it around, the stove stays off if you run out of energy.

Why 24V and not 12V in the living room?

Whether the living room should have a 24V or a 12V electrical system was a long-discussed question. If you look at it from the perspective of redundancy, two 12 volt batteries connected in parallel are more reliable than two batteries connected in series. If one battery fails in the 12V system, you still have a second one.

If the vehicle has a 24V network, you need a converter to charge the onboard batteries while driving – this can also fail, is expensive and charging the 24V starter batteries when stationary or even jump-starting from the onboard batteries is difficult or not possible.

For smaller systems, a 12-volt Renogy LiFePO4 system with BMS 12-200 is super easy to set up and quick to install. For 24V systems, you need the Mini BMS or (or VE-Bus BMS if a MultiPlus is needed). The construction of a 24V system with Renogy lithium batteries is a bit more complicated due to the external BMS. Still, it has the advantage that many Renogy inverters can be controlled via remote input.

Since the currents are 50% lower at 24V, smaller and, therefore, cheaper devices can be used. Practical example: A 12V 60A solar controller costs €556, and the 24V 35A controller only costs €333.

I would absolutely avoid building a 24V grid and then running the 12V water pump and the 12V fridge with a DC-DC converter. That brings an unnecessary source of error into the house. If 24V, then right!

Pros and cons of 24V vehicle electrical systems in trucks

12V starter battery

  • Small systems up to 2000W discharge power
  • Some 12V devices are already available

24V starter battery

  • Starting from the onboard battery
  • Some 24V devices, such as solar controllers cheaper
  • No B2B charging converters required
  • Thinner cables = less weight
  • Makes sense for large systems

I chose 24V because, with four batteries, I have enough redundancy to compensate for up to two defective batteries. I can start with the onboard batteries in an emergency. After converting the alternator, I could even do without starter batteries completely, which would save weight again. Thanks to 24V, the necessary cable cross-sections are smaller, saving weight, and some devices are cheaper.

Series & parallel connection of 4 batteries

If you have four batteries wired to 24V, there are two ways you could connect them:

It’s twice the same, but not the same! The sketch on the left shows four different voltages in the batteries. In the right picture, however, only a maximum of two different voltages, since two batteries are connected directly to 400Ah blocks and only then are connected in series.

The BMV712 battery computer has a second measurement input that can be used for various purposes. Either use it to measure the starter battery voltage, temperature or midpoint voltage of a 24V battery, which is the most interesting value for me. This way, I can monitor whether the two 12V 400Ah banks are drifting apart.


We have been using it since 2019, and I am very satisfied with the system. All wishes were fulfilled or even exceeded.

The idea of the two inverters was excellent because the devices no longer got in each other’s way. Today the Phonix Inverter Smart is also available as a 3000V model, and I’m considering whether I might still exchange it. Then the coffee machine could run and the heater simultaneously – which would be very practical when you get up in the morning.