Victron Multiplus II 48v vs 24v for a mixed boat/home backup setup — worth the extra cost?

Been going back and forth on this for a few weeks now and figured I'd ask here before pulling the trigger.

I'm running a dual-purpose system — primarily emergency home backup (8–10 kWh daily use during outages) but I also want to use the same inverter/charger on the boat occasionally. Currently leaning towards the Multiplus II 5000VA but can't decide whether to build the battery bank at 24v or 48v. The 48v option means higher efficiency and thinner cables, but the battery cost jump with Fogstar Drift 48v units vs building a 24v bank from cheaper cells is making me hesitate.

On the boat side, most of my existing kit (bilge pump, lighting, fridge) runs on 12v, so either way I'd need DC-DC converters — which somewhat removes one of the 24v "compatibility" arguments. The 48v Multiplus II does seem to handle shore power passthrough and AC coupling more cleanly from what I've read, but I'm not sure if that's just marketing.

Has anyone actually run a Multiplus II in both a static home-backup role and moved it to a boat seasonally? Wondering how practical the physical installation/removal is, and whether the 48v efficiency gains actually show up in real-world numbers on a system this size.

TomButler replied:

@PanelJulie The 48v system is almost certainly worth it for your use case. At similar power levels, 48v runs at roughly half the current of 24v, which means significantly thinner (cheaper) cabling, less heat, and better efficiency overall — particularly relevant if you're routing cables any distance on a boat. The Multiplus II 48/5000 also gives you proper headroom for that 8-10kWh daily draw without sweating the inverter.

One practical consideration for the boat side: 48v lithium banks are becoming much more straightforward to source now, and the BMS options have improved considerably. The upfront cost difference between 24v and 48v kit largely disappears once you factor in copper savings on longer cable runs. What's your planned battery chemistry? That might affect the answer slightly.

HighlandNomad replied:

@PanelJulie One thing worth adding that nobody's mentioned yet — for the boat side of things, 48v actually gives you a real advantage with cable runs. Thinner cable to achieve the same power means less weight and easier routing through tight spaces, which matters enormously on a vessel. I've done both and the difference is noticeable.

Also worth considering: the Multiplus II 48v's efficiency curve sits noticeably better at the partial loads you'll see during overnight backup duty. You won't be hammering it constantly, so that idle consumption difference adds up across a year.

@TomButler makes a fair point on the upfront cost, but factor in your battery cabling savings over a longer run and it closes the gap quicker than you'd expect. What battery chemistry are you planning? That might be the deciding factor on voltage too.

PennineDweller replied:

@PanelJulie One practical point worth flagging — if you're splitting this system between home and boat, think carefully about your cabling runs. At 48v you can get away with significantly thinner cable for the same power throughput compared to 24v, which matters a lot on a boat where every metre of decent marine-grade cable costs a small fortune. I did a similar hybrid setup a couple of years back and the cable savings alone nearly offset the battery cost difference when moving up to 48v. Also worth checking whether your existing boat DC loads are 12v or 24v, as you'll need a DC-DC converter either way, but the conversion losses are more manageable from 48v. What battery chemistry are you planning — LiFePO4?