I see articles about “adapting to life on board”, and as part of this, having enough power to relax and enjoy living on board can be an expensive challenge. The thing is, you can produce, store and use power far more cheaply with a 48V system than a 12V system.
If your boat is currently configured for a 12V start / 12V house / 230V AC setup, transitioning to a 12V start / 48V house / 230V AC system is actually very straightforward. You can keep all your existing 12V loads exactly as they are, your boat’s systems don’t need to change. The only real difference is running a 48V house battery bank and feeding those 12V systems through a DC-DC converter.
Once you make the switch, running a washing machine, cooking, and making water all at the same time becomes completely normal.
Why 48?
There’s a common misunderstanding that low voltage is more efficient. The opposite is true. Low voltage means high current, and high current means big losses in cables and connections. Modern residential AC appliances are often more efficient than 12V gear, more easily available and far cheaper.
Nominal 48V has become the standard for most serious off-grid and house battery setups. It’s the highest “touch safe” voltage, and the higher the voltage, the higher the efficiency. The same copper wires can carry 4x the power, and 48V can be 16x more efficient than 12v, as losses are the square of current. While 12V is very common on boats, it is not some magical ideal – cars used to be 6V, that’s now long gone too.
What we have on SV Razzle Dazzle
We have made Razzle Dazzle a little special. I wanted living aboard to be “easy”, so we have 5.25kw solar, 10KW inverter, a 30kwhr battery and 9KW alternators. No genset. We run air conditioning 24/7 over summer, no propane, all electric cooking, nearly unlimited water, electric hot water, and we don’t worry much about power. If we need more power and the sun is limited, we (very rarely) turn on an engine and make 7-15KW from the alternators. I added a new deep freezer last season for €130 retail, it’s not “Marine”. All this on a real blue-water performance cat that we have cruised on for six years. Having 48V makes this practical.
Purchase cost examples
If you’re looking to make the conversion, or are wondering what the price difference is between a 12V and 48V system, this will give you a rough idea:
12V System
| Voltage | Item | Model | Qty | RRP ex Tax | Total RRP |
| 12V | 5000W Inverter Charger | Victron MP-II 12/5000 | 1 | €1,873 | €1,873 |
| 12V | 2500W Solar Controller | Victron MPPT 100/50 | 4 | €197 | €788 |
| 12V | Alternator 3.5KW | Balmar XT250 Alt | 1 | ~€1,290 | ~€1,290 |
| TOTAL | ~€3,951 |
48V System
| Voltage | Item | Item | Qty | RRP ex Tax | Total RRP |
| 48V | 5000W Inverter Charger | Victron MP-II 48/5000 | 1 | €844 | €844 |
| 48V | 2500W Solar Controller | Victron MPPT 150/35 | 2 | €197 | €394 |
| 48V | Alternator 5.4KW | Mahle MG1 Alternator* | 1 | €750 | €750 |
| TOTAL | €1,988 |
Batteries are priced by capacity, not voltage, so for most brands 12V 400AH of battery is a similar price as 48V 100AH battery, both having the same capacity. Thinking about brands, Victron, LiTime, Wattcycle, Epoch and many others support and sell 48V systems.
If you have 4 x 12V LFP batteries already, and your manufacturer supports it, you may be able to simply swap the cables from 12V parallel to 48V series. BUT, read the manufacturer specs, as balancing must be considered. Whilst I prefer a single 48V battery, Victron fully supports 4 x 12V to get 48V.
*Note the Mahle Alternator; testing shows these can put out much closer to 7KW and be cooler than the Balmar XT when running at 2.5kw. The difference is amazing!
Running Costs – 5 kWh into the batteries – 4X cheaper
I also like to estimate running costs, thinking forward to what the system will cost over time.
Generator (6 kVA) running costs for 5 kWh / One Days Power (1kwhr makes ~100L of water)
| Voltage | Charger | Time | Fuel + Maint + Depr |
| 12V (360Ah) | 60A Charger | 8.5 hrs | €16.30 |
| 12V (360Ah) | 2.25 kW MultiPlus | 2.25 hrs | €6.50 |
| 48V (90Ah) | 3 kW MultiPlus | 1.5 hrs | €4.20 |
| 48V (90Ah) | 5 kW MultiPlus x 2 | 1 hr | €3.40 |
Alternator running costs for 5 kWh
| Voltage | Alternator | Time | Fuel + Maint + Depr |
| 12V (360Ah) | 80A | 6.5 hrs | €65.00 |
| 12V (360Ah) | 250A | 2 hrs | €15.60 |
| 48V (90Ah) | 140A | 0.8 hrs | €4.50 |
Where do these numbers come from? Your generator manual. Manufacturers publish fuel burn by load charts, so add in a generator lifespan in hours, the price of fuel and service intervals, and you can make your own cost table.
At 48V the same energy goes in with far less engine runtime.
Less fuel, less wear, and lower maintenance on the alternator and generator. Why? Diesel’s need good loads to be efficient. It’s very difficult to have enough load at 12v, so the engine burns more, wet stacks and carbon builds up. With 48V, the charge rates are a closer match to the engine efficiency curve. You get less engine hours, and a cleaner running engine with longer life.
Most LFP battery brands specify charge rates up to 0.5C (2 hour, 0% to 100%) with some allowing 1C (1 hour 0% to 100%) charging. Charge rate is rarely a problem with LFP, and with 48V the cabling is practical.
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- Alternator charge rate during testing
How a normal 12/12/220V boat becomes 12/48/220V
You don’t have to rewire the boat. In fact, most of your existing 12V systems stay exactly as they are.
By running a 48V lithium house bank and a 48V inverter, you can use a DC-DC converter to charge your existing 12V system. For solar, many Victron MPPT controllers automatically handle 12V, 24V, or 48V, simplifying the upgrade.
Because current is much lower at 48V, your existing main battery cables between the bank and the inverter can often carry three to four times the power they could at 12V. This means any required DC wiring changes are often minimal.
An electric galley with no propane/LPG, using normal residential appliances, is a huge saving and convenience. An AC watermaker is cheaper than a DC one, more reliable, easier to get parts for, and with conversion losses, has comparable power consumption.
Common questions
But I don’t want to convert my whole boat!
You don’t need to – everything that’s already 12V stays 12V, and the DC-DC charger just feeds it from the 48V bank.
Isn’t it hard to find parts in remote locations?
48V is actually the off-grid standard, and there are far more 48V inverters around than 12V ones. Since most off-grid systems run 48V, Victron and other brands have good availability of chargers, inverters, and batteries.
Who can work on it?
Any decent auto or marine sparky who’s done a few lithium jobs can handle it, although consider any insurance implications there may be. Lower current actually makes the wiring side easier in many cases.
Is it safe?
48V nominal is still considered touch-safe, and the lower current means less heat in cables and smaller fuses needed. Managing very high current with huge cables (as you do on 12V) is often more challenging.
Where do I get 48V solar panels?
You don’t need special panels for 48V, just wire two normal panels in series so the voltage suits the MPPT.
What about 24V?
24V is generally no real saving over 12V, and it’s not a common off-grid standard. It’s often harder to find good 24V equipment than 12V or 48V.
What if my 12V start battery fails — you can’t parallel it with the house bank?
That’s true, you can’t parallel them. On Razzle Dazzle, I run a Victron battery monitor on my start battery so I always know its condition. The start battery is kept perfectly charged 24/7 by the DC-DC charger and monitored through my Cerbo GX. I also carry a small portable lithium jump starter, but I’ve never needed it.
I see some equipment at 48, 54, 56 and 58V. What’s that about?
Nominal 48V runs charge voltages up to 58V depending on the equipment. That’s normal and is regarded by most standards as “nominal 48v”.
By Paul Young
I have been designing and building off grid systems for remote mine sites for 25 years and cruising full time with my family on Razzle Dazzle since 2020. One of our main criteria was "enough energy to be easy". That means lots of solar and a system that can be like living and not camping. I think we achieved that.
