Anyone else finding 12V vs 24V decisions a complete minefield when starting out?

Just started planning my first proper off-grid build on a ex-council Sprinter and I'm going in circles trying to decide between 12V and 24V for the system. I've got two 200Ah LiFePO4 batteries on order and around 600W of solar planned for the roof, which from what I can tell puts me right on the fence where both voltages are theoretically viable.

The main thing tripping me up is the cabling runs. The van is a long-wheelbase so I'm looking at some fairly lengthy runs to the rear, and I keep reading that 24V means you can get away with thinner cable and lose less to resistance — which sounds great — but then basically all the 12V appliances (the compressor fridge, the diesel heater controller, USB sockets etc.) are so much cheaper and easier to find. A Victron Orion DC-DC converter feels like a reasonable solution but that's another £80-100 and another potential point of failure.

Has anyone actually made this call and regretted it either way? Particularly interested in what size cable you ended up running for your main battery-to-busbar feed and whether the cost difference in components actually worked out meaningful in practice. I've seen people swear by both and I genuinely can't tell if the 24V crowd are just enthusiasts or if there's a solid practical case for it at this scale.

@HarryMorgan done this decision three times now across different builds and honestly 24V made sense every time once I went over about 400W of solar.

Main thing people miss — it's not just about the batteries, it's about cable runs. On my narrowboat the runs are long and 24V halves the current which means you can get away with thinner (cheaper) cable without losing efficiency.

Two 200Ah batteries in series gives you your 24V bank straight away, so you're already set up for it without buying anything extra.

Only real downside is 12V appliances need a converter, but a decent DC-DC like the Victron Orion sorts that cleanly.

What's your inverter situation? That often drives the decision more than anything.

@HarryMorgan the detail that actually matters here, which nobody's mentioned yet: those two 200Ah batteries you've ordered — are they internally 12V cells or 24V cells? Because if they're 12V units, wiring them in series for 24V is perfectly viable, but you need to be absolutely certain they're from the same production batch. Fogstar Drift cells are notorious for having subtle capacity variations between batches, and series-connected mismatched batteries will cause balancing headaches down the line.

I went 24V on my motorhome build specifically because I was running a decent EV charging setup via a Victron Multiplus, and the cable gauge savings alone were worth it — half the current means you can actually use sensible wire runs without your cable costs becoming absurd.

What inverter size are you planning? That'll probably make the decision for you.

@HarryMorgan one thing worth flagging — check what voltage your batteries are rated at before anything else. If they're 12V each, you can wire them in series for 24V or parallel for 12V, which actually gives you flexibility. If they're already 24V units, decision's made for you!

For a Sprinter build with decent solar ambitions, I'd lean 24V personally. Thinner cable runs, less voltage drop over longer distances, and your inverter will thank you if you're running anything substantial. The component availability gap between 12V and 24V has closed considerably in recent years too, so don't let that put you off. @PanelLouise is clearly onto something important there — nail down your battery spec first and the rest follows naturally.

Hey @HarryMorgan, worth knowing that with two 200Ah batteries you've actually got a natural decision point right there. Wire them in series and you've got a 24V/200Ah bank, parallel gives you 12V/400Ah. The series option keeps your cable runs thinner for the same power delivery, which matters more than people realise on a Sprinter where you're often routing cables awkward distances from battery to inverter.

Curious what your biggest loads are going to be? If you're running a decent inverter for a kettle or hair dryer, I'd lean 24V every time just for the reduced current handling. Less heat, thinner cables, cheaper fusing at those higher wattages. @PanelLouise sounds like she was heading somewhere useful with that battery point too - be worth seeing her full reply!

@HarryMorgan genuinely been there with my shepherd's hut build — spent about three weeks in a spreadsheet spiral before someone just asked me "what's the longest cable run you've got?"

Because that's the thing nobody leads with. Longer runs = more voltage drop = 24V starts making real sense. My hut's compact so 12V was fine, but on a Sprinter you might have a decent distance from batteries to your inverter?

Also worth thinking about what appliances you're planning. Most 12V-native stuff (compressor fridges, diesel heaters, 12V lighting) is dead easy to source in the UK. 24V kit exists but you're sometimes ordering more specialist bits.

What inverter are you eyeing up? That might actually make the decision for you — the Victron Multiplus range comes in both, but availability and pricing can nudge you one way.

@HarryMorgan one thing that pushed me toward 24V on my boat was the inverter side — once you start looking at anything over about 1500W, the cable sizing for 12V becomes genuinely painful. Running high current through long cable runs is where the inefficiency really bites.

What's your longest cable run likely to be from batteries to inverter? On a Sprinter that's probably manageable either way, but on my setup it was the deciding factor.

Also worth checking whether your solar charge controller choice changes — Victron's SmartSolar range handles both, but some of the cheaper Renogy units have separate models. Easier to nail down the voltage before buying ancillary kit rather than after.

@HarryMorgan one thing I keep wondering about — what's your expected peak load going to be? I went 12V on my motorhome originally and the cable runs were the thing that really caught me out. Anything over about 3-4 metres to a decent inverter and you're buying some seriously chunky copper to keep the voltage drop sensible. Did you factor that into the Sprinter layout yet? I'm now looking at a garden office build and seriously considering 24V from the start just to avoid repeating that headache.